Heroku Nginx HTTP 413 entity too large
Perhaps a bit late, but in order to fix this, move your client_max_body_size 10M;
outside of the location section. Like this:
client_max_body_size 10M;location / { index index.php; try_files $uri $uri/ /index.php?$query_string;}
See https://github.com/heroku/heroku-buildpack-php/blob/beta/conf/nginx/heroku.conf.php#L35 for reference on how heroku includes this file.