Hi Alexander,
From you first sceenshot, I found you website is ps-speicher.de.
Did you also authenticate ps-speicher.de instead of ps-speicher?
In addition, I found that when I try to open ps-speicher.de, the link in tab display https://www.ps-speicher.de for a moment.(very short time)
Then when I open your page with form(https://www.ps-speicher.de/crm.php) , I found another fact:
By default it displays https://www.ps-speicher.de/crm.php
When I selected then unselected link, the link became to https://www.ps-speicher.de/crm.php
So I think we might had found a key, from what I've found,
it seems that your page is actually hosted on www.ps-speicher.de(a subdomain) instead of real root domain(ps-speicher.de).
My thought is that actually we open your web page via www.ps-speicher.de, but then your web server redirects us to ps-speicher.de.
In other word, the www.ps-speicher.de might had been overwriten by ps-speicher.de.
Subdomain will be treated individually by Marketing application even if we have authenticated root domain.
Please try following steps for final approach:
In settings of your domain provider,
1. Add TXT record for subdomain www.ps-speicher.de.
2. Add 2 CNAME records for www.ps-speicher.de.
(You might need to append www after namekey1_domainkey, e.g: namekey1_domainkey.www as Host, but we won't need to change Value)
Send confirmation request for www.ps-speicher.de.
Once two fields got confirmed, then open your page to check whether it could display.
Regards,
Clofly