When trying to connect to my postgres server in Azure from psql client, I get the following error, even though I am using the correct username. How can I fix this?
psql: FATAL: Invalid Username specified. Please check the Username and retry connection. The Username should be in <username@hostname> format.
As noted in the error text, you are required to follow the <username@hostname> format when trying to connect to postgresql server, whether you are doing it from psql client or using pgadmin. Using <username@hostname> format instead of just <username> should get rid of the error.
Read the quick-start documents for Azure portal and CLI to understand more about how to create and configure your postgres server.