@nprofile1q... Any visits to the payment page without a ref, or an unregistered one could be tracked in your system but not trigger any payment split.
I don't think there'd be any concern about fraud here because it's all about paying podcasters.
Yes, someone could visit the payment page and manually add the "ref" code, but that just means someone else is paying to that app.
"Worst" case is that a podcaster includes the ref by default and that podcast app gets the fee from payments not thru app.