Update:
Apparently it was a problem with the bank of the credit card we've used, so really bad timing :)
I've just linked a Stripe account with Odoo eCommerce and it is failing on the first transaction attempt (on production, not in test), on the 3D Secure step.
I am pretty sure the verification codes (received via SMS or mobile phone app from the bank) are correct.
The only suspicion I have is that in the attempt we've been trying we've set also a company_name and VAT on the order and used a Company issues credit card, but I see that Odoo sends to stripe as the "Charge to" the name of the person, and not the company name.
So could be this a reason to fail 3D Secure ?
If the "charge name" does not match the name on the credit card used (which is a company one) ?
It's the only reason I can think of, but I doubt I am the only one facing this issue.
PS: it's latest Odoo v18 CE with default Stripe integration.