No. There's no minimum to join, and we have campaigns for creators of every size.
When you apply, accounts with over 1,000 followers on the campaign's network have the best chance. Under that, you'll see a note that it may affect your selection chances, but you can still apply.
Some brands set their own requirements for a campaign. If you don't meet them, the button reads "Not Eligible To Apply". Look at other open campaigns instead.