I can’t play in blitz Swiss tournaments?

Every time I join it says registration not available even though it’s open?

Hmm, which tournament(s)? Do you have a link?

Does it say that for every official tourney?

If so, you'll probably want to open a ticket.

https://support.chess.com/article/346-contact-us

1. Some tournaments registration starts one hour before.

2. Other reason sometimes happening is that you need to be in a certain group/team tournament to play certain torumanent.

3. Third reason: your ranking does not suits requrements.

4. If it is daily chess sometimes you need have already finshed certain amount of games 

5. In daily tournaments you have to many games wchich you lost on time

other reason I don't know

6. If swiss tournament is already stared you need to wait for next round to start