"Error: TypeError: Failed to fetch. Does the server allow CORS?status: undefined"

After spending many hours on this problem and still having no solution, maybe someone knows how to do the configuration on the IIS correctly, or knows a workaround in AppGyver.

The closest piece of information I found on this so far, which is an indicator why it’s not working was this:

According to that and other sources, the IIS on the Server is now set to:

According to what I read, the “Access-Control-Allow-Origin” can not have multiple origins. Then the term “Vary” has to be used. At least that’s my understanding.

The headers response I get in Postman is this, where the API is also working perfectly fine.

The response I get in AppGyver is this

Hello, You may want to check the network trace from your browser just to make sure the error you are receiving with Appgyver Data Source integration is a CORS-related one. And if this is so then your only option is to have your API CORS-enabled. I hope that helps.

I just tested the exact same API call with Thunkable and it was no problem. I guess that will be my next destination.