Заголовки может что не так, чего не понимаю.
Заголовки из браузера из примера запроса js:
OPTIONS http://selhom.ru/r.php
Ответ
HTTP/1.0 200 OK
Server: nginx-reuseport/1.21.1
Date: Wed, 01 Feb 2023 09:32:30 GMT
Content-Type: application/json
Content-Length: 53
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: GET,POST,OPTIONS,DELETE,PUT
Access-Control-Allow-Headers: *
Connection: keep-alive
Запрос
OPTIONS /r.php HTTP/1.0
Host: selhom.ru
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:109.0) Gecko/20100101 Firefox/109.0
Accept: */*
Accept-Language: ru-RU,ru;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Access-Control-Request-Method: POST
Access-Control-Request-Headers: content-type
Origin: null
Connection: keep-alive
POST http://selhom.ru/r.php
Ответ
HTTP/1.0 200 OK
Server: nginx-reuseport/1.21.1
Date: Wed, 01 Feb 2023 09:32:30 GMT
Content-Type: application/json
Content-Length: 13
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: GET,POST,OPTIONS,DELETE,PUT
Access-Control-Allow-Headers: *
Connection: keep-alive
Запрос
POST /r.php HTTP/1.0
Host: selhom.ru
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:109.0) Gecko/20100101 Firefox/109.0
Accept: */*
Accept-Language: ru-RU,ru;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Content-type: application/json
Content-Length: 86
Origin: null
Connection: keep-alive