Even though you believe you've only created one development certificate, Apple limits each individual developer to two active iOS Development Certificates per Apple Developer account.

How to Fix It

-Log into your Apple Developer account:
-Go to: https://developer.apple.com/account/resources/certificates/list

-Navigate to the “Certificates” section.

-Filter by "iOS Development" type.

-Revoke old/unused development certificates.
-Be careful here—only revoke ones you’re certain are not in use, or you'll need to regenerate and reassign them in Xcode or Keychain later.

-Create a new certificate after cleaning up the old ones.