Client Payments: Splitting a Payment Between Two or More Parties
When a client has one or more contacts associated with their record, or for a couple / conjoint /family client record, any credit cards associated with those contacts or members are also available to use when collecting payment, regardless of who is assigned as the billing contact. For example, in the case of divorced parents, each parent may be a contact for the child and you may collect separate credit cards for each parent to split the bill.
To do so, when adding a client payment, the contacts or members of a client will be displayed in separate tabs for your to select for a partial payment amount.

Select the partial amount and the tab of the person whose credit card you wish to use for payment. You may manually collect payment for each contact or member of the client.
Note: If you are using Autopay, only a single billing contact can be used. Therefore, split-billing can only be done manually.