Cross domain cookie problem

I have a cross domain cookie problem.
I have a site (lazertag.be, our site), when a customer makes a booking on this site he is redirected to our booking page (lazertag.checkfront.com, this site is our external reservation system, external site).
When the payment is completed the customer is redirected to a thank you page on our overarching site (facetheaction.be, our site).

I want the customer to see only 1 cookie banner and the cookie settings to be taken over.
(Cross-domain cookie consent, the settings of Lazertag.be should therefore be taken over by facetheaction.be).
(FYI: lazertag.checkfront.com is our external booking system and does not show a cookie banner)

If I do nothing, the customer will simply get a cookie banner twice (once on Lazertag.be and once on facetheaction.be (both websites are WordPress websites with the Complianz premium plug-in).

That’s why I followed the instructions on this page:
https://complianz.io/cross-domain-cookie-consent/
(I added “update_option(‘complianz_active_policy_id’, 20);” to the theme’s functions.php).
When I do this, there is no effect (still 2 cookie banners)
I think I still have to set the root domain somewhere.

That’s why I did the following:
On facetheaction.be ==> Complainz > setup > general > “enable cookiebanner on the root domain” > filled in “lazertag.be”

When I do this, I see still 2 cookie banners, but the cookie banner on facetheaction.be no longer works properly (it always sets itself to “functional cookies only”, no matter what you choose)

What am I doing wrong, how do I solve this?

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