HTTP headers too long error message

The error message

HTTP headers too long

suggests that your request has quite long header field(s). Although HTTP RFCs do not clearly stipulate a maximum allowed length for a header field or a maximum number of the header fields (to my knowledge), normally, an HTTP server implementation enforces a certain limit. My casual test suggests that the limit is somewhere around 4000 bytes (I sent a very long User-Agent value).

Will you post the exact request and reply? Please include the complete header sections and body for both. Copy&paste of the curl commands you execute would be helpful. If the data is too long to post, you can truncate: but please add the number of bytes.

You stated that the amount of data (which is the body part of the HTTP request) sent in the

POST

request might be too large, so the error message might be a red herring, though.