If you cannot cancel mail that you’ve sent, that means the cancellation window on your account has elapsed. Our API is designed to process mailings on a continuous, real-time basis, very much like email. Once mailings are processed, they get intermingled with tens of thousands of orders from all our other customers so it is difficult to pull them back.
To catch any problems upfront, we recommend upgrading your account to take advantage of the cancellation window feature. You can adjust this window to a time that works for you so you have time to cancel on your end. If you do not wish to upgrade, then we recommend having your developer write buffer time into your Lob integration that gives you time to cancel before submitting a request to Lob.
If you were unable to stop a check sent through Lob, you can still prevent it from being deposited by contacting your bank and placing a Stop Payment on the check. This can be done by contacting and providing your bank with the check number.