You need to be a company administrator in QuickBooks to add applications.
There are two different user roles in QuickBooks that have these permissions, the “Master Administrator” or the “Company Administrator” role type.
Note: Credentials for QuickBooks Online Accountant may not work as they don't necessarily imply admin rights over the individual company files, you will need to use company credentials.
If you need to import on behalf of the client, then you will need to ask the client for their credentials, or log into their QuickBooks account and manually upgrade your permissions from the 'Manage Users' drop down menu.
From there they can either invite you as an accountant or create you as a new user with 'Company Administrator' privileges.