[2021] Couldn't connect to subscription server

No real idea, I"m sorry! I guess make sure steam.exe and eu4.exe are allowed through all your firewalls.

If that doesn't help, probably best to lodge a support ticket at paradox.zendesk.com  

filip133 said: I don't have menu like this "DLC Subscription" :/ Someone can write me why? How can I buy subscription? :/

It is not available to all users. It is essentially random who sees it and who does not.This is because it is an experimental programme.  

MrScrosh said: i am having the same problem right now, is there a solution

Make sure you have the Steam Overlay AND Steam Cloud Sync enabled.