Problem joining webinar on android as panelist with unique link

I've been trying to help someone with an Android wanting to join our webinar as a panelist with a unique link

He gets a screen with a Launch button half hidden and can only join via a browser.

This works , but his volume is low and of course not as many features.

Anyone come across this before?

He uses zoom often on his android and has never had a problem.

When we tried a regular meeting link it worked fine. Webinar unique link ... can only join via browser.

Tried restarting phone - same results

I didn't gather more info as I didn't want to take up too much of his time - and we have a work around - joining via the browser with headphones seems to work sufficiently.
I'm just left puzzled

Thanks Massimo