I recently tried adding a day old walmart receipt to my account & it said barcode invalid. This is odd considering yesterday I had no problem adding the same receipt to my "Fetch" Rewards app. I feel as if Ibotta doesn't want to give rewards back very easily. If I have anymore issues I'm uninstalling my Ibotta app.
Sometimes offers are pulled when a predetermined number are claimed. And they also have expiration dates of course.
Regardless the reason, this seems to happen to me late evening between 10 PM and midnight eastern time.
If you had the offer in your list for WM open up a ticket. Usually they are very good in these situations. Send in pic of upc with receipt.