How can I get round the CORS issue (Self Hosted)

[SamB-GB]

I have this self hosted but still encounter the CORS issue when on sub domains...

Access to fetch at 'https://sub.mydomain.com/' from origin 'https://sub.mydomain.com/' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.