I have recently posted about my confusion with understanding the difference between internal and external users. I now understand the difference (your model is similar to Trello, Miro, and so on).
Part of the confusion was caused by the fact that, although we paid for one subscription (= 1 “user”), we had 3 users active - “had” in the past tense of the word. These 3 users were added when we first signed up for the SeaTable account and continued to work after we signed up for one user in the Enterprise Plus account. This has now changed. I see that in the admin area a new list of users has appeared, one active, the other two inactive.
As a test, I clicked the switch to activate one of the deactivated accounts and was immediately informed that the annual subscription fee would be debited from the bank account. There was no option to confirm that I wanted this to happen. I then deactivated that user but still saw that I have two users available.
Question: have I activated a second user account only for that specific user or have I activated 2 user accounts that we can share (as long as only 2 users are active)?
I would sincerely request that you look at this process again and ensure that the option is there to confirm billing before proceeding and not immediately be billed.
I think you should offer the chance to pay for blocks of users rather than a subscription fee per user. I believe it is in your interest because most organisations will try to limit the number of users as much as possible knowing they will be billed for each user, whereas if I know I have, say, 5 or more users for, say, 50 euro a month, I will be more willing to pay that and get used to the price - there is then no incentive for me to keep costs down and you will get more income per customer.