CORS policy prevents REST service POST from Snap app preview in Chrome browser

Hello SOTI team, I am developing an app with SOTI-SNAP wherein I use javascript to use a AspNetCore REST service from our server located on the internet.When developing I use the preview function of SOTI-Snap in the browser (Chrome). Calls with the GET method works from preview. But the POST method returns the following error in the browser console: Access to XMLHttpRequest at 'https://[OurServer].com/soticlean/TimeRecords' from origin 'https://s3.eu-central-1.amazonaws.com' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: It does not have HTTP ok status. Here my Javascript call from my app: var settings = { "url": Snap.variables.getValue("gvarServiceURL"), "method": "POST", "timeout": 0, "headers": { "Content-Type": "application/json" }, "data": JSON.stringify( { "deviceUid": data.deviceUid, "date": data.date }), }; return $.ajax(settings).done(function (response) { console.log(JSON.stringify(response)); alert(JSON.stringify(response)); }).fail(function (response) { alert(JSON.stringify(response)); }); } And here the customHeader section from my Web.config of my AspNetCore REST Service: ... <system.webServer> <httpProtocol> <customHeaders> <add name="Access-Control-Allow-Origin" value="https://s3.eu-central-1.amazonaws.com" /> <add name="Access-Control-Allow-Headers" value="Content-Type"/> <add name="Access-Control-Allow-Methods" value="GET,PUT,POST,DELETE,OPTIONS" /> </customHeaders> </httpProtocol> .... I hope someone can help me. Thanks a lot Martin