Friend is invited for a long time but can't access the game.

[p.tatarov]

About a few weeks ago I sent an invite to a friend in Deadlock, but he never got access to the game, and I still see in the game that the invite is in the queue. It shows as "pending", but he can't join.
Here's his Steam ID: https://steamcommunity.com/profiles/76561198224755880/
Thanks for any help