To connect a Beatport or a Beatsource account, be sure to have an active paid LINK subscription enabled to this account. Without it, we will not be able to access to APIs of these services.
If you have a LINK subscription but still not able to connect your account (login seems working but then you are disconnecting); you have to contact => support@beatport.com (explaining that you can't connect your account to Soundiiz and they will be able to fix that for you).