Cannot update/upgrade Debian install due to repo signature

[orange2]

Installed from ISO for a local SBC. Cannot run apt update successfully due to repo signature. See screenshot. Anyone know how to fix this please?

 

[SteveITS]

3CX recommends not installing updates at the command line because it may install OS updates not tested with 3CX. So essentially, AFAIK, we're not supposed to run updates on an SBC...?

 

[orange2]

Fair enough! Thanks for the guidance