I'm also having trouble getting CumulusMX to play with Home Assistant.
HA works fine, pasting a manual request into the browser using the key works fine, and I have generated a key for each app, but I cannot get cumulusMX to do any more than the initial request.
IS yours working OK?
is it possible to make CumulusMX play nicely with Weather-display and both of them access the weatherflow data?