This is the final URL :
https://sitekit.withgoogle.com/v2/site-management/setup/?code=sitekit-qqRRYrtx93bnvmTEyLDppS&site_id=HJqSwU9W4B6b5b7wsX4Eq8-Zej4jhBzMJizEGRUYZ5MMM.apps.sitekit.withgoogle.com&step=delegation_consent
I have more than one site on the same VPS and I face the same problem in all of them. I think the problem is an error in the plugin, knowing that it is the first time running on these sites, so I had not used this plugin previously.
I implemented the site title step and it did not work either.
This message appears to me at the beginning of the setup, and I do not know if the problem is due to it:
Looks like the AMP CDN is restricted in your region, which could interfere with setup on the Site Kit service.