At the moment there is no way to match a payment against invoices that belong to different customers. An example of this requirement is if you receive cheques from different customers and batch them into a single deposit slip for banking purposes. When the deposit clears in your bank account, it typically shows as a single amount rather than an amount for each cheque. The recommended approach for this is as follows
1. Create a new bank account called 'Deposits Clearing' or something similar.
2. For each cheque to be batched in the deposit, enter an Invoice Receipt in the bank account created in Step 1 above. The new bank account should eventually have a balance equal to the total of all the cheques being deposited.
3. When processing your bank statement, enter the deposit as a General Receipt and select the 'Deposit Clearing' account as the offset account. After saving the transaction, the amount from the bank statement should reduce the balance in the 'Deposit Clearing' account to zero.
4. Optionally reconcile the clearing account.