Correct format for remote mysql server

Silly question, probably. What is the correct format for a remote mysql server?

define('DB_SERVER', 'db5009893440.hosting-data.io');

I've tried server different formats, but none will work:
//db5009893440.hosting-data.io
//db5009893440.hosting-data.io/
https://db5009893440.hosting-data.io/

I've checked the settings with the host and the address is correct.

The one you have does look correct to me:

define('DB_SERVER', 'db5009893440.hosting-data.io');

but it's been years since I have seen one of these.

Me too, that's why I'm asking. Before I go yelling at the host, I want to be sure I configured it right. :-) Thanks!!