Walmart receipts can be rescanned within 24 hours. If it has been more than 24 hours, you will have to open a request.
Also, if you have your Ibotta account linked to Walmart, you can get that message. You cannot submit a receipt that was linked to your Walmart account. It is done automatically. if anything is missing, you will have to open a request.
Still an issue...
Mines ok but yesterday it took 3 tries to get a Walmart receipt to upload.