I don't know the answer. However it's first time VPN claim they can give onion address (rather than allow or can access onion address without Tor Browser).
Seriously?
I have been using NordVPN which has the ability to connect to an onion server. I've already managed to access onion addresses, in Chrome.
But connect to/access onion address and giving onion address (also called Tor Hidden service) are two different thing though. I briefly read NordVPN's page about Tor/onion, but there's no indication they setup Tor Hidden service for their VPN users. And FWIW, accessing onion address without Tor Browser offer less privacy since your browser have unique fingerprint.