"Invalid hostname" error

The actual error

If you see errors like

or

you are in the right place!

Checklist

1. Check the domain you join with

In this example we say that we want to join to our server using play.example.com. I set up a CNAME record on play.example.com correctly, the problem is that I forgot to add it to our domains tab in our panel.

2. I did not add both SRV and CNAME domains to our panel

If you have an SRV record pointing to another CNAME e.g. _minecraft._tcp.example.com (SRV) pointing to play.example.com (CNAME) you need to register both play.example.com and example.com in our panel.