How to make a webhook that adds a secondary group to a user

[nigeld27]

After struggling for months to find a developer who can help me create a webhook, I'm wondering how hard it is to make it myself. Using the Zapier integration to create a 'trigger', I would like to add a secondary group to a user. I have no development experience however I am quite good at Zapier and configuration.

 

Has anyone else done this themselves? Or can someone direct me to a guide for this? I found this thread below but at the time there was documentation on webhooks available. Has this changed now?