Mandatory Signup Fees
We don't currently have a mandatory payments option, but there is a workaround for groups which require membership payments before allowing access to the group content.
1) Set a required field on your registration form with only one checkbox, which acts as a confirmation for the payment (It might read something along the lines of: 'I agree to pay membership fees of $x.xx').
2) Create a Unpaid member list with a filter to contain all members with "Yes" selected in their 'I agree to pay membership fees' database column.
3) Create a 'Paid' list on to which you will manually put any member who pays for membership.
4) Edit your group's settings to be set in such a way to allow access to your various site features only to members of your 'Paid' member list, so all other visitors will be limited to viewing your homepage.
5) Add a 'Payments' widget to your homepage from the 'Layout' page, with a description informing members that they must pay before being added to a group. You can also e-mail payment requests to members if you prefer.
6) Assign a manager to check subscription payments and manually add newly paid members to your 'Paid' list.