The server was not able to access the page to analyse your content – Error 500

[paulAtSlim]

• I've read and understood the contribution guidelines.
• I've searched for any related issues and avoided creating a duplicate issue.

Please give us a description of what happened.

I get the error:

The server was not able to access the page to analyse your content

When trying to fetch https://xxxxx, a 500 status code was received. Please make sure your server can access the page.
In the Backend.

I've tried to dig down the Rabbit hole to find more detailed Error and ended in the PreviewService and the getContentFromUrl Method.
There the RequestFactory call, when I remove the Header part:

'X-Yoast-Page-Request' => GeneralUtility::hmac(
   $uriToCheck
)

it works.
I tryed to figure out for what the header is required but could'nt figure it out.

I don't know why it throws an error and only on subpages and not on all. And for what is the Header?

Additional context

It only happens in Subpages. The Rootpage works.
It's a Multisite TYPO3 Setup

Technical info

• TYPO3 version: 11.5.39
• Yoast SEO version: 9.0.3