docs: update errors.md - add JWEDecryptionError (#7855)

* Update errors.md

Added detail for an JWT_SESSION_ERROR. JWEDecryptionFailed

* Apply suggestions from code review

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Co-authored-by: Balázs Orbán <[email protected]>

Author: wroscoe

docs/docs/errors.md

@@ -136,6 +136,8 @@ The `callbackUrl` provided was either invalid or not defined. See [specifying a
 
 #### JWT_SESSION_ERROR
 
+JWEDecryptionFailed: NextAuth.js needs `NEXTAUTH_SECRET` environment variable to encrypt JWTs and to hash email verification tokens. This can also occur if you have changed the `NEXTAUTH_SECRET`, but you still had an active session with the old secret. Logging in again solves the issue.
+
 JWTKeySupport: the key does not support HS512 verify algorithm
 
 The algorithm used for generating your key isn't listed as supported. You can generate a HS512 key using