I appreciate your time in reaching out to us here, Abdawa.
We currently have an ongoing investigation about the error message when upgrading the subscription from Essentials to Plus. Our engineers are working on resolving the issue as soon as possible.
While we're unable to provide a workaround, I recommend reaching out to our Customer Care Team. They can help add your company information to the notification list. This way, you will be updated when the issue is resolved.
If you have the new QuickBooks Assistant help update, you can follow these steps:
Once the issue is resolved, you can follow the steps in this article to upgrade: Upgrade or downgrade your QuickBooks Online subscription.
Thank you for your patience. If you have any other questions or concerns, please let me know in your reply. I'll be around to help. Stay safe!