Screen mirroring from MacBook Air M3 to Fire TV

I watched a movie or two with screen mirroring from my MacBook Air to our Fire TV, but suddenly there's no picture--sound is fine. I've restarted both; both are on the same WiFi network, etc. I tried another streaming service, but that didn't change anything. I'm trying to watch movies through our library on Kanopy and on Hoopla. What to do?