Add subscribe form to landing page with proper domain

Oh, we use stripo as email builder. Instead i diasbled enabled all the content builders and when i retried it it worked properly and the captcha.
Yes, that's the way to do it. I asked for a support ticket and access, just to make sure that this is the issue, but you did well, so no need.
Clearing the cache cleared left overs maybe?
There are a lot of assets to publish and the subscribe form is the subject of that cache. Normally you should clear the cache only after some update in the code.
EDIT: The landing page was has a custom domain different from the main domain and has proper SSL configured yes
Then you should be fine. This was a issue on our side.