Your Portal customers can now access the Billing Portal even if they haven't accepted their invitation email!
All you have to do is give them a Management Link. These links can be fetched by you, the merchant, from our Admin UI (see screenshot below) or API. They are also available on the statement emails that can be sent to customers.
Note: if the customer has not yet accepted their invitation, in order to fully access Portal they will still have to click on a link that we send to their email address on file - this is a security measure to ensure that Management Links are only usable by the customer. But, this verification process can be initiated from the Management Link. So, the customer can now basically auto-invite themselves, beginning with only a Management Link.