I am looking to get the altium footprint for ATSAMR21G18A
Why have you posted in an AVR/UC3 forum then?
I'll move this to an ARM section.
That question is best asked on an Altium forum. Does Altium not have it already in their libraries? It is a standard footprint. In the time taken to ask the question and wait for a reply you could've easily created the footprint!
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