How do I submit an expense claim for multiple purchases?

To put it simply, you can't.

Each purchase needs to be entered separately into ExpensePlus through the Purchases module screen to make sure the full details of each receipt are captured and allocated correctly.

The system is designed so that each transaction has one Supplier or Payee, with one receipt or invoice, allocated to whichever expenditure categories you choose.

When you enter multiple purchases in ExpensePlus, as separate transactions, you will still get repaid in one payment. Once receipts have been checked and purchases have been approved, ExpensePlus automatically combines expense payments for each payee on the 'Payments Screen'. 

To help you better understand the Purchasing module as a whole, please visit the module overview page here.