How do I deduct expenses for promotional expenses for my customers and/or for providing travel reimbursements to my customers?

My business is an interactive software company (mobile gaming app) that creates online travel agency gaming concepts, I want to give my customers/users a travel reimbursement for purchasing a getaway experience on our website/in-app, valued at $499.73, which goes towards their tourism bookings with participating vendors within our game app/ecosystem; but $20.73 of that transaction is a technology service fee for related businesses expenses required for payment processing and/or operational expenses. I want to be able to write off this transaction as a deductible business expense or promotional business expense. How can I do this?