Antigen tests are fine at larger airports but I have heard of people facing problems at smaller airport. Last week I was flying IXD-DEL & there was an argument going on at the next check-in counter for a passenger flying IXD-DEL-ORD. They were not willing to accept the antigen test & he was tying to explain to them that it was allowed. I didn't hang around long enough to find out what happened in the end.