Add postback URL to wordpress page

Hi,

We receive traffic from a traffic supplier;
user arrive on our page with URL with utm_queries

example:
https://domainname.com/lander/?utm_source=1234&utm_medium=102b36a47f51423bd037bf51dr34&utm_campaign=test

This page is an age gate - to confirm he's above 18 - then he's redirected

We need to fire this postback url once the user confirm hes 18 and is redirected:

http://tracking.networkpunch.co.uk/aff_lsr?transaction_id={utm_medium}

This is basically to signal to our traffic supplier that the user he sent us can be counter as a conversion as hes valid and he confirmed his age

The {utm_medium} placeholder need to be replaced and dynamically populated with the value passed on the url in the utm_medium parameter

In our example:
102b36a47f51423bd037bf51dr34

So basically, send a http request to:
http://tracking.networkpunch.co.uk/aff_lsr?transaction_id=102b36a47f51423bd037bf51dr34
if user confirmed hes 18 and is redirected