You may share multiple estimates and invoices with your customer using the same exact information link.
The Job information is what controls the one or more documents your customer will see when they connect to you.
If there is only one estimate, then the customer will only see one estimate. If you send a second estimate, then the customer will be able to toggle back and forth between the original estimate and the second estimate to see the differences.
There is nothing you need to do to make this happen. MyOnlineToolbox sees when multiple communications are tied together at the Job level and automatically makes it easy for your customer to review and compare.
SPECIAL NOTE: The above screen is what the contractor sees when using the MyOnlineToolbox platform. The above screen is not what the customer sees. The Connecting To Your Contractor section in the User Guide provides the visual of what a customer sees.