HTTP Response Code 403 returned
The 403 response code is returned when a GET request includes a body or a content-length header.
This commonly occurs when a client employs a single cURL session for multiple requests, and a GET request follows a prior POST or PUT request. By default, cURL accumulates request headers and includes all headers from preceding requests. Consequently, a POST or PUT request appends the content-length header, and the subsequent GET request is transmitted with this unintended header.
To avoid this issue, use the --next option in subsequent requests (curl_reset in PHP). This ensures that the headers are appropriately managed, preventing the inadvertent inclusion of headers from previous requests.
Are HTTP header names lowercase or Pascal-Case?
According to HTTP/2 standard, all headers are lowercase.