Ok, so I randomly selected some letters, numbers and special characters for my Azure SQL Server user password and ended up with %3 as part of that. I published my ASP.NET Core project from Visual Studio. So far so good.

When running the project I got an error: System.Data.SqlClient.SqlException: Login failed for user ‘myuser’.
I couldn’t figure out why. I knew I had the correct password so I went to publish it again and checked all the settings. What I noticed was that in my connection string in the database part of the publish settings was that the %3 had been removed. I typed it in manually, published and everything worked.

Now, I don’t want to manually fix my password everytime so I changed my password and now I don’t have any problems anymore.