Android TWRP not flashing using ADB; FAILED (remote: ‘unknown command’)

I am trying to install TWRP on a UMX u683cl and I get an error when trying to flash it using ADB.

Phone Specs:

Error Message:

C:UsershanieDesktopAndroidplatform-tools>fastboot devices
2e0331  fastboot

C:UsershanieDesktopAndroidplatform-tools>fastboot flash recovery twrp.img
Sending 'recovery' (4562 KB)                       OKAY [  0.147s]
Writing 'recovery'                                 FAILED (remote: 'unknown command')
fastboot: error: Command failed

C:UsershanieDesktopAndroidplatform-tools>fastboot boot twrp.img
Sending 'boot.img' (4562 KB)                       OKAY [  0.147s]
Booting                                            FAILED (remote: 'unknown command')
fastboot: error: Command failed

I have done lots of research on the problem but cannot find a solution because the phone is not very well known.

Thank you.