Before You Begin
Make sure that you have Removed the Add-In/SPFx from Site Contents
You need to be a Site Collection Administrator in order to do this step.
Step 1: Go to Site Settings
Step 2: Go to Site Collection Recycle Bin
Note: If you are on a Sub Site, you need to Go to top level site settings first
Step 3: Delete ShortPoint.Online App from the Recycle Bin ( If it Exist )
If you have removed ShortPoint.Online app from Site Contents recycle bin, then you might not find the App in this recycle bin,
In case it is here, just delete it.
Step 4: Delete the App from Second-Stage Recycle Bin
From the same recycle bin, you will find a link at the bottom called "second-stage recycle bin", click on it.
And delete ShortPoint.Online again from this Second Stage Recycle Bin