Hey @PaulHyes-0550,
I looked at the MEM admin center right now and I can configure my Autopilot profile to just %SERIAL%, no prefix needed in my case. I didn't run a deployment now but it is accepted. So, did you fail to save the Autopilot profile or did it fail during deployment?
best,
Oliver Kieselbach | Twitter | Blog
Mark useful answers by clicking "Accept Answer", many thanks!