Issue
You are using SharePoint 2019 On-Premise environment and trying to add the ShortPoint SPFx app to your Site Contents. Once you are selecting ShortPoint SPFx to add you receive an error:
Reason
You are logged in using a System account. SharePoint policy does not allow adding apps using the System account.
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Solution
Please, log in with a non-System Admin Account and make sure that that account is the site collection admin.
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