Most Pay Ahead methods work directly from QBO -
Selling and Redeeming Gift Cards in QBO
Another Option you have for Gift Certificates - Pay ahead or other forms of Gift Cards is QBO Credit
1) you will need to decide if you want the Credits to Auto apply or not.
2) You can create an invoice inside of QBO and Charge the customer via Your CC processor
3) You can Then Apply Credit Memo's to customers through QBO
4) Depending on your Credit settings inside QBO (step 1) it will automatically apply those credits to the customers job, or you will manually apply them when the time comes