Please could you send us a copy of the latest backup log? This can be found in the UpdraftPlus Existing Backups tab.
The contents will be too long to post here directly, but you can use an online service such as Dropbox or Pastebin, and post the link here.
What happens is it says the backup can’t be completed to OneDrive becasue I haven’t purchased the add-on. I DID purchase the add-on. In WP-Admin it says to “click here to configure the add-on or it won’t be usable.” When I click it it just goes right back to the same page.