Checkbook Quit Working!

We’ve bought checkbook a few years ago and out of the blue it quit working today.

Says: “CheckBook quit unexpectedly."

Application Specific Information:
*** Terminating app due to uncaught exception Mac App Store receipt validation error, reason: Cant check receipt signature: No valid signer’

Were we supposed to pay for the upgrade to fix the snafu just a couple months ago?

We’ve got version: 2.5.8

Thanks for any input

pjw10500 about CheckBook