Cors Not Working Anymore

I'm having a strange problem that from one day to another my AJAX requests for a website not working anymore. I'm now struggling to get it working and can't find the problem. this

Solution 1:

Yvo Cilon made me think about the multiple values. And pointed me in the right direction.

I searched for headers and noticed that on the webserver there was a header already set and I added it in my code.

I removed the header set in the webserver to have control on how and when it is used.

Thanks for sharing your thoughts.