A Limited Company has sent me an invitation to use their quickbooks account but when I log in I go into the other limited company that I already do the books for.

Once the invitation is accepted, the account is added to your client list, jessgjini.

Our system detects that your email address already has a QuickBooks Online account associated with it. That's the reason it lets you sign in instead of signing up. Let's check if the account is added to your client list by following the steps below:

1. Go to this website: https://c4.qbo.intuit.com/qbo4/login?&useNeo=true&region=GB.
2. Enter your user ID and password.
3. Click on Sign In.
4. In the attached screenshot below, click on the company account under the QuickBooks Accountant. 
5. On your Dashboard, click on the Go to client's QuickBooks. (See the second screenshot). 

If not, let's make sure to complete the invitation setup, jessgjini. Please open the email sent by QuickBooks Online, and select the user ID you'd want to use. Sign in and then click on Accept Invitation. Once done, log in to your QBOA account again. 

Keep us posted if you have any questions.