Hi,
I had the exact same issue but I figured this out.
The thing is that the “dom” parameter is somehow overwritten.
So, to display both extensions, you need to add :
"dom": "BWlfrtip"
in the “custom commands” of your table:
the B stands for the buttons extension
the W stands for the filterwidget extension
Maybe you would have to add some other letters according to your needs.
Cheers
