Web Browser view:
Step 1: Click "Completed Orders".
Step 2: Choose the order you want to receive the payment for.
Step 3: Click "Generate Sales Invoice".
Step 4: Find the DO you want to be paid.
Step 5: Click "Payment"
Step 6: Choose Email invoice to your customer. Click "Send Invoice".
Customer will receive an email notifying them on the invoice with a "Pay Now" link.
By clicking "Pay Now" customer will then be redirected to the payment checkout session.