Yes, unfortunately it still gave me the "Error 413 Request Entity Too Large" problem.
i think this error has to do with compatibility, you seem to be trying to flush a firmware that your control board does not support, and it throws that error before even going into flushing state, you need to try another firmware, try the once for S9j not the S9, or use another firmware that's not from bitmain, i think any non-asicboost firmware should work.