SQL Server 2019 License Issue Fix

I'm seeking an expert to resolve a login issue with SQL Server 2019. We transitioned from a trial of SQL Server 2018 to a licensed version. After entering the authorization code, we encountered an error stating "the server was not found or was not accessible." We've confirmed that the server and instance names are correct, and no network or firewall changes were made.

Ideal skills and experience:
- In-depth knowledge of SQL Server, particularly version 2019
- Experience with SQL Server licensing and authentication issues
- Strong troubleshooting skills for connectivity problems
- Familiarity with network configurations related to SQL Server

Please provide a brief outline of your approach and relevant experience.