client intended to send too large body

Not knowing the version of your nginx build and what modules it was built with makes this tough, but try the following:

1. Copy your client_max_body_size 300M; line into the location / { } part of your vhost config. I'm not sure if it's overriding the default (which is 1 MB) properly.

2. Are you using nginx_upload_module? If so make sure you have the upload_max_file_size 300MB; line in your config as well.