Have you tried to connect to QBO and got the following error message;
This is happening because someone else using that QBO file already has a link with the Invitbox App. Seeing QBO only currently allows one user to have the connection you will need to get that user to disconnect so you are able to make the connection.
To do this they need to login directly to Quickbooks Online with their email and password. Then as the image below shows click on 'Apps' on the left hand side.
Then at the top of the screen click 'My Apps'. Then the Invitbox App will be displayed and you can click 'disconnect' from underneath it.
You will now be able to make your connection from Invitbox to QBO.
Oops an error has occurred. Error Code: app_already_purchased Message: The application has already been subscribed to by another user for this company. Please contact xxxx to make changes to this subscription.app connected to another user