Unable to run "make px4_fmu-v3" on a Custom github branch

I am using Ubuntu 20.04.
I have tried to run the make px4_fmu-v3 command on one of the custom branches but it keeps throwing an error (attached screenshot).

along with:

I installed the entire px4 toolchain for Ubuntu/Debian Linux here.

I still am not able to work around this issue.

Any comments or suggestions?