Tips after Service

If a client pays through Scritches pay are they able to leave a tip after the booking? I have folks pay prior to the booking and do not want to tip at that step in the process, which is totally understandable, but it looks like they don’t have the option to add a tip afterwards. I do give the option of plenty of other forms of payment, but wanted to get a solid answer. I wouldn’t mind the payment sort of being on “hold” until the end of the booking. Which is what I think these big apps do on their end.

I’m trying to give the opportunity for a tip without being tacky or pushy!