That is really peculiar. As per my DM, I removed my partner as a travel companion and then tried to share and got the same £0 charge displayed.
I didn't send him any more Avios though
It's odd that the GGL team don't know the sharing route via the shopping portal.
I wonder if it's a location thing? You're being billed in EUR whereas I see GBP. That's the last straw I think to clutch at.