Thanks for your question
As per Microsoft document, https://learn.microsoft.com/en-us/azure/postgresql/single-server/quickstart-create-server-database-portal#create-an-azure-database-for-postgresql-server
|Server name||A unique name that identifies
your Azure Database for PostgreSQL server. The domain name postgres.database.azure.com is
appended to the server name that you provide. The server can contain only
lowercase letters, numbers, and the hyphen (-) character. It must contain 3
to 63 characters.|
| -------- | -------- | -------- |
||
Or you can try creating server using az postgres server create command.
Let us know if this works!
Thank you.