Hi @monika-sadlok_5031,
That error means that the ProGet application container cannot make a network connection to the the SQL Server container.
I would try to restart the containers, start with SQL Server. Make sure it's running. If it's running, you can try connecting to it with another tool like SSMS if you'd like to verify.'
Otherwise, on the ProGet side, you can only configure the connection string; upgrading or changing the license key has zero impact on this. If it worked in the past, then it means that the SSQL Server container is not running or your network/container configuration changed.
This can be hard to discover exacgtly what changed, so I would recommend "starting from scratch" on a new server/environment, then compare/contrasting what changed. Sometimes it's as simple as a typo or an errant - (dash character) in the wrong place/script.
Cheers,
Alana