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.

Solution

Please, log in with a non-System Admin Account and make sure that that account is the site collection admin.

Related articles:

• ShortPoint SPFx Installation on SharePoint 2019 (First Time)
• Installation Step 2: Add ShortPoint SPFx to Site Contents (SharePoint 2019)