You can add a payment link as part of one of your application questions, but it wouldn't show up as a hyperlink so you would need to ask the applicant to copy and paste the payment link into a new tab in their browser. 

If the payment link is through PayPal, for example, you could say something like: "Please note that we have a $25 fee for all applications submit. Please copy and paste the link below to make payment prior to submitting your application. Once you have submit your payment, please copy and paste your PayPal confirmation number into the box below”. Then you could create a free text box for the payment confirmation number.