Access to XMLHttpRequest at has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource

My domain using port 2087 using https socket.io and ok everything. This morning I change port that does not support https. But when I rechange to 2087, the following error occurs. Why could I solve this?

Access to XMLHttpRequest at has been blocked by CORS policy: No ‘Access-Control-Allow-Origin’ header is present on the requested resource.