I am really sorry for the inconvenience.
The mentioned issue occurs when the user trying to install the app does not have permission to approve app charges. Only store owners or staff members with "Approve app charges" setting enabled can approve Shopify app charges. "Approve app charges" setting can be enabled by the store owner under Shopify Admin > Settings > Users and permissions.
The issue will be fixed in the next release. Instead of showing an internal error, a new page explaining the error will be shown.