I would say that you could not use it. The reason is because when you are using PayPal for example, the payment success script is run when payment is completed, PayPal notifies Membership Pro about the payment. It's a server to server notification, so even you use Joomla system message, users won't see it
If you use subscription stored script, then, it should be possible. But for subscription success script, I don't think it's possible if you use payment method like PayPal
thanks for the prompt reply. Just to confirm my intended PHP script run by the php plugin has nothing to do with payment but posts info to an external api and will return a success or failure response.
Last edit: 1 month 1 day ago by Chris Preece. Reason: Spelling