If you want to pass some custom value in the checkout page URL and get the values in the thank you page/hosted page by API response.
Then you can add that value on the checkout page URL and send that full link to your customers
For example –
“&hello=workingonpage” is the extra value with the checkout page URL.
When your customer completes the transaction they will be redirected to the thanks page or the hosted page and your extra value will be seen on the URL of the thank you page.
You can catch that string from the thanks page URL and call for the verify hosted page API for getting the details of that customer.
Link for the API – https://www.pabbly.com/subscriptions/api/#section-31
The form data for calling API will be the query string.