Hello, ttbfinancialserv.

I appreciate taking the steps provided by my colleague to become their accountant. I'll share additional information to successfully add your client to your QuickBooks Online for Accountant account. 

To be sure, did you received the email invitation at the email address associated with your QBOA account? Any information can help me provide the best solution in solving your problem.

If it ask you to create or set up an account, you may have other QuickBooks Online companies open in your browser windows or tabs. You can sign out and then accept your client's invite. If the issue persists, let's manually open the email invite since you may be experience some web browser issue.

Here's how:

1. Open the invite email.
2. Right-click the Accept Invitation link and copy the web address.
3. Open a new private web browser. In Google Chrome, this is called an Incognito Window. For other browsers, it's a Private Window or Private Browser.
4. Right-click the address bar and paste the copied web address.

It will ask you to sign in. Fill in with your user ID and password you use for your QuickBooks Online Accountant firm.

Additionally, the client's invitation will expire after 30 days. If this happen, advise them to delete the original invite. Then, they can send a new one. Share with them the steps below:

1. Sign in to QuickBooks Online.
2. Go to Settings ⚙ and select Manage users.
3. Select the Accounting firms tab.
4. Look for your accountant firm.
5. In the Action column, select the small arrow ▼ icon and then Delete. 
6. Once done, then can send a new invite.

For your reference, you can also utilize the client notes feature if you want to keep or add important information about your client. Check out this resource for more details: Keep client notes in QuickBooks Online Accountant.

You're welcome to post again if you need anything else in QuickBooks. We're here to help you.