Your version is past EOL. You should upgrade to either the latest version or the current LTA (long-term active version) at your earliest convenience. Your upgrade path is:
Currently we are using SonarQube 9.1 version. I think we purchase the license for the 9.1 Developer Edition version. If we update to 9.9 or 10.5, will it work without any issue or again, do we need to buy the license for 9.9 or 10.5.
Do you Know because of the 9.1 EOL version is the reason for this 0% code coverage issue? Please reply asap.
Your license is for an edition, not a version. We wouldn’t do anything to discourage you from upgrading because we want you to keep up with active versions and get the benefit of the latest features.
You can freely upgrade and your license will still support it.