I always get error when sync.

Fetching project aosp/platform/external/checkpolicy
Fetching project android_device_oneplus_bacon-1
Fetching project android_external_exfat
Fetching project aosp/platform/external/stlport
Fetching project aosp/platform/prebuilts/tools
Fetching project ubuntu/platform-api
Fetching projects: 0% (1/172) Fetching project aosp/platform/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9
error: RPC failed; result=22, HTTP code = 503
fatal: The remote end hung up unexpectedly
error: RPC failed; result=22, HTTP code = 503
fatal: The remote end hung up unexpectedly
error: RPC failed; result=22, HTTP code = 503
fatal: The remote end hung up unexpectedly
Fetching projects: 1% (2/172) Fetching project android_external_libselinux
error: RPC failed; result=22, HTTP code = 503
fatal: The remote end hung up unexpectedly
error: RPC failed; result=22, HTTP code = 503
fatal: The remote end hung up unexpectedly
Fetching project aosp/platform/prebuilts/misc
error: RPC failed; result=22, HTTP code = 503
fatal: The remote end hung up unexpectedly
error: RPC failed; result=22, HTTP code = 503
fatal: The remote end hung up unexpectedly
error: RPC failed; result=22, HTTP code = 503
fatal: The remote end hung up unexpectedly
error: RPC failed; result=22, HTTP code = 503
fatal: The remote end hung up unexpectedly
error: RPC failed; result=22, HTTP code = 503
fatal: The remote end hung up unexpectedly
error: RPC failed; result=22, HTTP code = 503
fatal: The remote end hung up unexpectedly
error: Cannot fetch aosp/platform/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9
Fetching project android_hardware_samsung_slsi_exynos5
error: Cannot fetch aosp/platform/prebuilts/tools
error: Cannot fetch aosp/platform/external/stlport
Fetching projects: 2% (4/172) error: Cannot fetch ubuntu/platform-api
error: Cannot fetch aosp/platform/external/checkpolicy
error: RPC failed; result=22, HTTP code = 503
fatal: The remote end hung up unexpectedly
error: Cannot fetch aosp/platform/prebuilts/misc

error: Exited sync due to fetch errors

Any clue about that?

Try to wipe storage. I do it on my oneplus one

@yug said:

Thanks again. Still not working for me. It says it's booting recovery, and boots to the OnePlus screen. I also let it sit for over an hour just to try, and when I reboot (hold down the power key) it boots to a OnePlus screen (presumably trying to reboot recovery again) and hangs. I let that sit for over an hour and reboot (hold the power key again) and it boots to Android.

I am not sure how it worked for you without booting into Ubuntu recovery to install. I understand it did work, just not sure how it's possible.

Edit: This is resolved for me. I reinstalled twrp and formatted my internal storage aka sd. Once done, installation succeeded without issue.

I tried it. erase all, and it's work