404 on Authorization Button Click

[SZChimp]

Describe the bug
Clicking on the "Authorize with Mautic" button leads to a 404 page.
The URL it tries to connect to is https://www.mautic-integration.sunzity.de/mautic/authorize the mautic instance is installed as seen in the screenshots.
Deleting the cache does not help.
I tried using HTTP, HTTPS and entering the TYPO3 Domain as Callback URI.

To Reproduce
Steps to reproduce the behavior:
0. Follow the installation process without any issues.

1. Click on "Authorize with Mautic" button

Expected behavior
I should be redirected to the login mask asking for permission to connect the TYPO3 to my account in the Mautic backend.

Screenshots

Additional context
The TYPO3 is installed in the web/ directory, one level above the mautic/.
TYPO3 10.4
EXT: marketing_automation version 1.2.3
EXT: mautic 4.0.1
The page is htaccess protected. Removing the htaccess protection does not help either.

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[SZChimp]

The API can be accessed by the URLs in the documentation, e.g. /mautic/oauth/v1/authorize but the button should lead me to the correct URL.

[xbouillet]

I have the same problem.
The URL of the button "Authorize with Mautic" is like https://www.xxxxx.com/mautic/authorize
She leads to a 404 page.
I have empty the cache.
Any ideas?
please