Connection problem from backend to frontend

I created an api in frappe framework whether i checked that in postman it working perfectly but i am using that api in react app but displaying these two errors

1). Access to fetch at ‘’ from origin ‘http://localhost:3000’ has been blocked by CORS policy: Response to preflight request doesn’t pass access control check: 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.