S21 debrand 3 phone with btu firmware

[Beans on toast Dave]

How do you debrand a s21?
In the past iirc it was just a case of flashing BTU Non carrier specific firmware
Now if I do the same the phone refuses to boot until I reload the branded 3 firmware back on
What do I need to do to put the non 3 firmware on?

Thanks

 

[Beans on toast Dave]

thanks for the replys, have asked at xda but no replys, its more helpful here