The message "This instance is not registered with Google Drive Plugin" is showing for embedded Google Docs

Summary

The message "This instance is not registered with Google Drive Plugin."is showing for embedded Google Docs.

Also, the following error is shown while trying to install "Confluence Google Drive":
UI:
The add-on host returned HTTP response code 500 when we tried to contact it during installation. Please try again later or contact the add-on vendor.

Steps to Reproduce

• Open a page that has a Google Doc embedded
  OR
• Try installing "Confluence Google Drive"

Expected Results

Add-on is installed and embedded files are loaded

Actual Results

This instance is not registered with Google Drive Plugin
or
This add-on cannot be installed without the Atlassian Connect framework. See our documentation for more information.

Workarounds

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