I think I should add some context...
I could not use
https://xdaforums.com/t/unlock-root-twrp-unbrick-fire-hd-10-2017-suez.3913639/ because my HD 10 is 5.6.8.0, I used the instructions here
https://github.com/3ch01c/3ch01c.github.io/blob/master/docs/how-to-setup-amazon-fire-hd10.md instead to get offline root via an exploit followed by installing SuperSU to maintain root. (the authors never meant to install a custom rom, only modify the current Amazon ROM so they did not unlock bootloader)
I proceeded to install the "official" TWRP app and in the "TWRP FLASH" was initially able to reboot into Amazon Recovery, but managed to mess something up so that the tablet won't reboot into recovery at all now (via the buttons or adb) just goes to black and white amazon logo, black screen, back to bw logo and fires up like normal (no recovery)
For a long time if I did "adb reboot bootloader" it would reboot into fastboot but keep disconnecting and reconnecting to the computer, but I think I was able to fix that today by installing the correct USB driver.
I just went into fastboot and tried "fastboot flash recovery twrp.img" and "fastboot flash recovery "TWRP_suez-180918.img"
I got the same error message both times
Booting Failed (remote: 'the command you input is restricted on locked hw')
I tried "fastboot oem unlock" and got the same error
Is there any way to get around this error?
I'm pretty lost at this point, is there any way to get TWRP working?