How to fix error "Failed to load ressource : Acces-control-allow-origin cannot contain more than one origin"

We have recently engaged an external company to develop a mobile application for us.

We've made an API available for them, but they're having problems compiling the iOS executable. (Everything works fine under Android)

The error message they receive is:

"Failed to load resource: Access-Control-Allow-Origin cannot contain more than one origin "

We use symfony 4, Nelmio CORS and a nginx configuration.

We added this to our nginx configuration, but the problem persists (https://enable-cors.org/server_nginx.html) ("Authorization" has been added on GET and POST method), and I honestly don't know what do I have to do to help them.

Do you have any idea about this? Is this a server problem? or a development problem on their side? on ours?

They use Cordova with ionic and WKWebView. WKWebView seems to cause problem once they've enabled CORS.

I've check my API response, and it's showing the good value:

I am at your disposal if you wish to obtain additional information.

This time it was not a server side issue.

Double Header Access Control => only when running command

ionic cordova run [android/ios] —livereload 

and accessing API, iOS problems :

Allow-navigation and Allow-intent added in confix.xml > iOS platform :

<allow-intent href="*" />
<allow-navigation href="*" />