npub14jydfl56dy849mwft0t7vgyp4036fs7unuajtf437u4u9n5fngushdr2yd (npub14jy…r2yd) Hi Pasquale! Currently, you need a custom domain in order to create an additional sub-user on your multi-user plan.
Additional sub-users under our brand domains (@proton.me, pm.me, protonmail.com etc.) cannot be created at the moment, but we're about to implement this functionality very soon, so please stay tuned to our social media channels for news!