Error: Header Redirection not working - Shared hosting with PHP 7/8

[PhillipRSA]

Thank you for the huge effort.
As a beginner I started as the top and slowly moved down the line.

I cannot find the Typo and there other Pages that has the same command and it works.

IONOS.com shared hosting is not willing to modify php.ini (output_buffering = 4096)
login.php line 56 = header("Location: ./dashboard.php");

Also Port:8888, they are not willing to Open so I just removed it.
What is the purpose of having Port:8888

Looking forward for some guidance.