You’ll have to check the limits parameters on all items between you and the server. Quite hard for proxy servers if any, but at least you can check:
Apache:
- LimitRequestBody, around 2Gb by default, maybe greater for 64bits, check error logs for details.
PHP:
- post_max_size which is directly related to the POST size
- upload_max_filesize which may be unrelated, not sure
- max_input_time, if the POSt takes too long
- max_input_nesting_level if your data is an array with a lot of sublevels
- max_execution_time, but quite sure it’s not that
- memory_limit, as you may reach a size exceding the subprocess allowed memory
- max_input_vars, if your data array has many elements
If you have reached the compiled in limit for Apache your only solution is to avoid direct POSt of such a big chunk of data, you’ll have to break it into pieces.