Trouble with lpr and Brother wireless printer

I use an HL-L2370DW which only accepts PCL on BINARY_P1.
I think it likely that yours acts the same. You'll have to tell lp to send
the output through a filter, using (iirc) the vf= option in printcap.
This is what i used for a filter:

#!/bin/sh
gs -sPAPERSIZE=letter -sDEVICE=pxlmono -sOutputFile=- -dBATCH -dNOPAUSE -

Hope this helps.