Hello @suguru, thank you for reaching out to our team, and sorry to hear about your invitation issue.
If you have reached a maximum of 10 free users on a free space plan, organization owner would have to add valid credit card details in order to go into overages.
In order to add credit card details, please follow these steps:
- Organization owner needs to log into the account
- Click on organization name in top-left corner > Organization settings
- On the right side of the screen you will see Your Payment Details section
- Click on Enter payment details
Alternatively, you can refer to the following article: Steps: How can I update my credit card details?
Hope this information helps!