Let me share some details on how you can install an app, Gail Baltimore!
You'll need to have either Primary Admin and Company Admin access to add a third-party application in QuickBooks Online. If you already have this access and still getting the same error, you'll want to perform some troubleshooting steps.
Let's start by using an incognito window and install an app from there.
- Google Chrome: Ctrl + Shift + N
- Safari 11 or newer: ⌘ + Shift + N
- Mozilla Firefox: Ctrl + Shift + P
- Microsoft Edge: Ctrl + Shift + P
Also, browsers save junk files called cache that can cause errors in QuickBooks Online so you'll want to clear them. Additionally, make sure that you're using an up-to-date browser.
For QuickBooks Online Accountant, you can add an app for your client within your account. Please check these links for more details:
Post again here if you have more questions. Take care!