I have never used Mac OS, can't help to get/install Android Tools. Maybe someone else can.

You must enable developer options on the device by touching said entry 7 times. Then "Developer Options" appear as a new top-level item in Settings. Inside, there's "OEM unlocking" it must be enabled so you can later, with working Android Tools, enter the command "fastboot oem unlock". This would be denied otherwise. When everything worked, the bootloader is now unlocked.

Once the bootloader is unlocked, you will see a message and a menu on every boot, as seen in this thread for example: https://forum.xda-developers.com/oneplus-3/help/help-how-to-remove-device-unlocked-t3425028
They fixed the typo in a later firmware (those ship with new OxygenOS releases but can be installed separately with TWRP later if needed for some reason). Should you already see this menu on your device on every boot, it means the seller has already unlocked it and you could skip all those steps and "just" need to get Android Tools working on the Mac.

  • AGI replied to this.
  • AGI likes this.

    KM Many thanks!

    Did you create a Nandroid backup?

    Meanwhile after various attempts I think I found the right "command line tools only" at https://developer.android.com/studio/releases/platform-tools
    The downloaded folder finally contains fastboot. That should be sufficient, no need to install software on Mac as I was doing at the start.

    • KM replied to this.
    • KM likes this.

        AGI

        AGI I assume making an Android backup is something I shall do via TWRP before flashing the custom ROM? Would that allow me to restore the OEM software in case something goes wrong or PA does not work for me and I want to return/re-sell the phone?

        I should be possible with this method. However, there's also the unbrick tool which allows you to recover the device from a total soft brick (black screen at boot). It needs Windows. I did that several times and can confirm it works. Basically it writes back every partition to the device's memory using low-level hardware access: https://forums.oneplus.com/threads/guide-mega-unbrick-guide-for-a-hard-bricked-oneplus-3.452634/

        As long as TWRP still works, you could also install any OxygenOS version with TWRP, which will overwrite even TWRP.
        And as long as you have fastboot access, you should be able to install OxygenOS via command line, too.

        It might be useful to know which OxygenOS version you are on currently, just in case it is a very recent version that brought some firmware changes (might break TWRP or some custom ROMs' install routine).

        • AGI replied to this.

              KM there's "OEM unlocking" it must be enabled so you can later, with working Android Tools, enter the command "fastboot oem unlock"

              Thanks, this piece of information was missing on that webpage!

              KM t might be useful to know which OxygenOS version you are on currently

              The OxygenOS version is OP3_O2_open_25. Android version is 8.0.0 and Android security patch level is September 1, 2017.

              I badly hope I won't need to reinstall it, but it is good to know there are options out there. Thanks!

                  Uhmmm, there is already a problem. I thought of checking I can use internet data within the original OS before installing PA. My SIM name is reported correct (with my Samsung Galaxy on5 from the US, no name would show up at all). However, I can't get online. I checked on the APNs ,and there are a bunch from Japan, but not mine. I am unable to create a new one specific to my carrier. From the little I read this option has disappeared after Marshmallow...
                  Furthermore, there are many posts from people who lost internet data after updating the software, e.g., https://forums.oneplus.com/threads/not-able-to-edit-add-apn-settings-in-op3.510771/, and they are not based in Asia...

                  Maybe PA will give me the chance to edit APNs?!?!

                  • KM replied to this.

                    AGI In the list of available APNs I see a "+" button, which allows to add an APN:

                    Not sure if this is what you'd need.

                      Yes, that is what I was looking for. Is that on PA? Thanks a lot! Then there is hope it does not work on Oxygen, but it will on PA.

                      I read drivers are not needed on Mac, but I am unable to see my phone upon launching ./fastboot devices.

                      When I reboot the phone and I choose fastboot mode, I do not have to anything else, do I? There is a green START in capital letters on top, then "FASTBOOT MODE" and "DEVICE STATE - locked" in red at the top and bottom, respectively, of a list of phone specs, like the product name and the serial number.
                      I just got the doubt I need to hit START...

                      • KM replied to this.

                        AGI Maybe you need to launch it as administrator/root, with elevated rights. I don't know anything about Mac OS, sadly.
                        Don't forget you'd need to put the device into fastboot mode first though, by holding down one of the volume buttons upon boot and then choosing fastboot. Not sure if it was up or down.

                        • AGI replied to this.

                            KM Thanks. I am in fastboot mode. No need to hit START. That restarts the phone in normal mode.

                            EDIT: I read that under Developer Options I should set Select USB Configuration to MTP (Media Transfer Protocol) rather than Charging, in order to be able to see the phone on the Mac. No improvement. However, every time I reboot from fastboot I see that the option has changed back to Charging...

                            2nd EDIT: Same happens if I simply reboot without going thru fastboot. The USB configuration automatically reverts to Charging. If it happens to you too, then that is not the problem. I guess I will have to try with a Windows PC...

                              I have been trying with a Windows 10 machine. The phone is not recognized. Among "Universal Serial Bus controllers" I find "Unknown USB Device (Device Descriptor Request Failed)". If I try to update the driver, Windows says the best driver is already installed. Under Properties I read "Windows has stopped this device because it has reported problems. (code 43). A request for the USB device descriptor failed". After a few seconds since the plugging-in, the unknown device disappears from the list. I tried to fix the code 43 error following this video, but the problem persists.

                              • I am not sure whether the cable is the problem. Sadly, I do not have a spare.
                              • In this video the guy confirms the USB configuration automatically reverts to Charging, which poses doubts on what the configuration is in fastboot.

                              PS: Maybe I should have started a new thread on this install, I apologize. Happy to help out to move posts in case the moderators agree.

                              • KM replied to this.

                                The reason you have to install the developer tools is to get an ADB-friendly driver. I have no clue how to do this on the Mac, but on Windows you absolutely have to install the driver or ADB/Fastboot won't see the phone at all.

                                • AGI replied to this.
                                • KM likes this.

                                  The Windows drivers might be on the phone's memory and you could install them right from the connected phone that shows up as a drive.

                                  • AGI replied to this.

                                    Thanks to both. I installed the two drivers found at

                                    https://gsmusbdriver.com/oneplus-3

                                    but it did not work.
                                    I already tried with a virtual machine on Mac. It can't see anything, neither an external hard disk.
                                    I will see if I can find a Windows 7 machine.

                                    KM The Windows drivers might be on the phone's memory and you could install them right from the connected phone that shows up as a drive.

                                    Interesting point. However, it is not that my Mac or Windows machine can't see the phone in fastboot mode only, they can't see it all.

                                    Gurm The reason you have to install the developer tools is to get an ADB-friendly driver.

                                    Do you mean I shall install the 1GB Android Studio from https://developer.android.com/studio?

                                    • KM replied to this.

                                          AGI I still think using Linux could solve this issue the fastest.
                                          With Ubuntu: open a console, type
                                          sudo apt update
                                          sudo apt install android-tools-adb android-tools-fastboot
                                          Manjaro:
                                          sudo pacman -Sy android-tools

                                              KM Uh, thanks, that sounds quite a stretch for my limited competences, and, also, I have only business devices around, so I need to watch out what I install...

                                              I just tried on a Windows 7 laptop, and the phone is not recognized because malfunctioning. Even after installing the driver. Same as on the Windows 10 machine.

                                              Other weird thing. I can't get online using internet data, as I said before. If I click on an existing APN setting, I am given the option to edit, I just realized, but the edits are not effectively taken into account. So, no improvement. However, to my surprise, I called myself from Skype and the phone rang. Maybe to an expert it is obvious why, but with my T-Mobile Samsung this sim card was not good at anything.

                                                KM Versions of Android SDK tools from distributions are often disturbingly out of date.

                                                (Mainly referring to Debian/Ubuntu, no idea about Manjaro)

                                                  Guess what?
                                                  I used a different USB-to-USB-C cable and the phone got recognized!

                                                  ./fastboot devices
                                                  c0dcc5f0 fastboot

                                                  However, I am encountering another issue which is not detailed in the tutorial

                                                  ./fastboot flash recovery twrp.img
                                                  Sending 'recovery' (27529 KB) OKAY [ 0.631s]
                                                  Writing 'recovery' FAILED (remote: 'Partition flashing is not allowed')
                                                  fastboot: error: Command failed

                                                  Any idea what is wrong this time?
                                                  Shall I unlocked the bootloader before flashing TWRP? I would think so, although I do not exactly know what I am doing and in the instructions I am following the unlocking is not mentioned in such order. On the phone screen I read DEVICE STATE - locked in red.

                                                  • KM replied to this.

                                                    AGI You must enter "fastboot oem unlock" first, or you can't do anything.
                                                    Edit: I think it would delete all data but I guess you don't have important data on the phone's memory yet.

                                                    • AGI replied to this.

                                                        KM Thanks! I had proceeded meanwhile! I am wiping partitions with TWRP. In all the tutorials I have watched I can't see a partition called USB-OTG, which I do have in the list. I guess wiping it is meaningless since, if I understand, USB-OTG is just an external device connected to the phone via USB? None in my case!?

                                                        Doubt before wiping. Shall I back-up something? I mean, I have not used the phone yet, so I have nothing mine. But I wonder, if something goes wrong with PA, is there an easy way for beginners like me to reinstall oxygenOS using the created backup?

                                                        NOTE: In my case there has been a difference to the tutorials I went thru. After unlocking the device via fastboot, I could not turn the phone on in fastboot mode anymore. I had to restart the phone in normal mode as post-factory reset (go thru the choice of the language, fingerprint protection and all that) and tap again 7 times on the Build Number to re-gain developer privileges. Then Developer Options re-appeared among the settings. Inside I saw the OEM resulted unlocked, but USB debugging had turned to off.

                                                        • KM replied to this.
                                                            dev