Cors issue during Auth flow

Hi

During the last step of the Auth flow (Posting a form back to zendesk) I get a cors issue:
Access to XMLHttpRequest at 'https://xxx.zendesk.com/zendesk/channels/integration_Service_instances/editor_finalizer' from origin 'https://our-own-server.be' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

I was wondering if somebody had this same issue and how I can resolve this?

Thank you in advance

Kind regards

Ivan