Browser Print can't write to selected printer but detects it

I'm using Browser Print with a web application I've made, loaded in the JS for Browserprint.

The device is definitely being seen from the browser, as the select dropdown populates with the printer and a config info windows pops up.

However, I'm unable to writeselectedtext or sendimage at all.  I don't know how to begin diagnosing this issue, help would be greatly appreciated.

Zebra ZD410 thermal label printer.