Clubs have a certain level (starting at 0).
At level 0 you only have 10 seats to invite players, increasing the level increases the seats available in the Club.

The Club Leader can raise the Club level (but only after reaching the necessary Level Points).

Here are the Costs to uplevel:
  • Level 1 - 20 seats - cost 150 Level Points
  • Level 2 - 40 seats - cost 500 Level Points
  • Level 3 - 55 seats - cost 2000 Level Points
  • Level 4 - 80 seats - Cost 10,000 Level Points
You can see the Club level (and the Club Leader can also increase it) in the "Club Objectives" panel: