Best Practices for Storing GCLID

I want to implement offline conversion tracking for google ads. I’m getting a lot of leads that don’t end up booking but I currently only track incoming bookings.

What’s the best way to store GCLID when someone fills out a booking request on Wix’s booking system? Why doesn’t Wix automatically just store this information?? I want to use it so I can upload whether or not the lead led to a sale later on.

I tried following a guide with hidden fields but apparently that doesn’t work anymore.

Try Google Tag Manager

How?

Lets stay I pull the GCLID in tag manager and store it – how do I associate it with a booked client? How do i know which GCLID goes to which client?