Here in this troubleshooting guide, we’ll be sharing with you possible steps to Fix the Fastboot FAILED (remote: Command not allowed) Error while trying to flash files on your Android device. If you’re also facing the same problem, then don’t worry. Talking about the ADB and Fastboot commands, these are the most useful ways to easily flash zip files, booting your device to fastboot or recovery mode.
Additionally, you can install root access or other modules in order to get into the unlimited customizations of Android. Additionally, if your Android handset has stuck into the boot loop issue or in the bricked status, you can easily fix the issue by the flashing firmware file via ADB and Fastboot method. But it doesn’t mean that you won’t gonna receive errors while using it. Yes! ADB and Fastboot methods can also occur multiple errors.
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What is FAILED (remote: Command not allowed) Error?
It seems that one of the most common reasons behind such an issue is that you’re flashing a file to an incorrect partition. So, this can basically cause issues with the system partition such as the A/B slot partition. To be very specific, there is no recovery partition in the A/B partition. Therefore, you can’t flash the TWRP Recovery to the recovery partition directly.
Whereas if your device has the A-only slot partition, still it should be having the recovery partition. So, you can directly flash the recovery to the partition instead of booting it. But in most scenarios, not-so-geek users get confused with it and end up with the FAILED (remote: Command not allowed) error after trying the process wrongly.

what to if my handset is A only partiton