Need rule: if Giftcard used to pay order, then skip PayPal, if Giftcard not used then goto PayPal My Drupal Commerce site allows customers to buy vouchers (each voucher is a product), which are paid for using PayPal and which gives them a code. The system then allows them to book classes, using a voucher rather than PayPal. Using commerce giftcard module, customers fill out the voucher (giftcard) code in the giftcard pane at checkout. Apply the voucher and the the total to pay goes to zero and the voucher value is reduced by the cost of the class. Checkout says no payment is required, all is well, class is booked. 

However, when no voucher code is entered checkout still says no payment is required, even though the total is not zero. In this case I need a rule checking the total of the order, allowing no-pay-progress if total is zero (i.e. gift card has been applied) else require PayPal (i.e giftcard code has not been applied and total is > zero).And that is where I get stuck. Any help on how to formulate this rule much appreciated.
Payment methods are enabled via Rules. One of the Rules conditions is to check the balance of an order. Have you not tried adding this to your rule that enables PayPal as a payment method?