Trying to upload a document via PUT, getting error request_too_large/ Error Message: File is too large

Good afternoon,

I'm trying to set up a PHP script to do an import of files into Sugar and I'm running into an issue when trying to use the /Documents/:document_id/file/:file_name endpoint. I'm sending over my base64 encoded string ('test') as the contents of the file with an oauth-token header and 'X-Content-Transfer-Encoding' of 'base64', but Sugar is responding with:

{
"error": "request_too_large",
"error_message": "File is too large"
}
I've checked both the php.ini and sugar config and they both have fairly large limits set, so I'm stumped as to why Sugar thinks it can't accept this file and the API docs are unfortunately barren about doing this kind of operation.

Does anyone have some insight into how this is supposed to work and/or how I can post the contents of a file over to the API so it gets written into the system?