Swiss tournament. New participants cannot be added (there is no "participate" button")

We created a tournament in the club based on the Swiss system (lichess.org/swiss/Kt44BmFW). The tournament was created on November 13 (28 rounds). After some time, new participants can no longer be added to the tournament (after about 3 weeks). Are there any restrictions on such tournaments?

If a player has missed half of the tournament then the player can't join the tournament

The whole point of a swiss tournament is that you principally start and finish the tournament with the same players.

Thank you very much!