1. Sorry, you don’t have permissions to add apps here

Sorry, you don’t have permissions to add apps here

Sorry, you don't have the permissions to add apps here

You are lacking the required permissions to install the add-in.

In general you need to be a Site Owner (or have the permission to manage website) to install add-ins, but in the case of this add-in you need to be an administrator of either the tenant (access to SharePoint Admin Center) or the site collection.