Why is CORS triggered?

Question

CORS

in the browser from the page

http://116.203.177.252/product/obratnyi-osmos-raifil-r0905-550ez-1

I send a request:

GET /review?page=1&per_page=4 HTTP/1.1
Host: 116.203.177.252:3000
Connection: keep-alive
Origin: http://116.203.177.252
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/76.0.3809.132 Safari/537.36 OPR/63.0.3368.94
Accept: */*
Referer: http://116.203.177.252/product/obratnyi-osmos-raifil-r0905-550ez-1
Accept-Encoding: gzip, deflate
Accept-Language: ru-RU,ru;q=0.9,en-US;q=0.8,en;q=0.7
If-None-Match: W/"c79-vHO8ho+ARf56U9JUsZcNxY5NyTg"

in response the browser says:

Access to fetch at 'http://116.203.177.252:3000/review?page=1&per_page=4' from origin 'http://116.203.177.252' 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.

why is CORS triggered?

Answer 1

Because the port