First, did you purchase this in-store, Pickup&Delivery or Online?
I will assume you purchased it in-store. First, make sure the offer has been selected under Walmart in the Ibotta app and you have purchased the quantity required for the rebate. I always scan the UPC while in the store to make sure it matches.
If you already did this, you can go to Redeem at the bottom of the screen and scan the barcode of the receipt. The Ibotta app should find the item. If it doesn't, you can scroll down the list of other offers and select the item. It will ask you to scan the UPC. Once it has been verified, you can submit the receipt to Ibotta.
Walmart receipts usually credit your account almost immediately, but in rare cases it can take longer.