too many requests to add members

If you're referring to using sharing_add_folder_member to add a member to a shared folder, there is a AddFolderMemberError.rate_limit that applies per 24 hours. Please wait 24 hours and try again.

Otherwise, regarding any particular error you're seeing regarding files/folders on the Dropbox web site, please reach out to support.

Yes, I refer to sharing_add_folder_member. I use it as follows.

member_selector = dropbox.sharing.MemberSelector.email(<email_address>)
add_member =  dropbox.sharing.AddMember(member_selector,dropbox.sharing.AccessLevel.viewer)
members = [add_member]
dbx.sharing_add_folder_member(<shared_folder_id>, members)

Previously, it worked fine, but now the script runs endlessly. It doesn't return any error. Am I doing something wrong that doesn't return an error?
From the dropbox interface in the browser, it returns the error "Folder updates in progress. Please try again later."

Maybe there are some pending invites or I have been banned. But how can I check it?

The sharing_add_folder_member method should either return a result, or raise an exception. I can't say based on this snippet what is happening with your code execution flow, so I recommend stepping through with a debugger to see where it is hanging or infinitely looping. Let me know if something is broken in the Dropbox API/SDK itself when you do so and we can investigate.

In any case, I can only help with the API itself, so for any questions or help regarding your account state itself, please contact support.