You can get back to your work right after making the updates, parramatta.
To ensure that the new payment details went through, you can go back to the Billing and Subscription page. From there, the status of your QuickBooks Online subscription should be Subscribed.
Now if you're trying to add a new user, you can follow these steps:
Here's an article to help the user accept the invitation email: How to add, delete, or change user access.
If it's not a user that you want to add in QBO, just let me know. I'll help you set up their profile.