Hi @john23,
Welcome to the Auth0 Community!
Apparently, you’ve made some changes or started using a new SDK/Library that is using a different signing algorithm for your JWT Tokens. It is not matching the configuration you have on your Auth0 tenant.
To select the signing algorithm used in the ID Token, go to your application’s advanced settings and select JsonWebToken Signature Algorithm. The default and recommended algorithm is RS256:
More information about this topic can be read here: RS256 vs HS256 JWT signing algorithms