I'm guessing this is for a Walmart transaction and you had your Walmart and Ibotta accounts linked at some point? If so, this is because Walmart will automatically send us transaction data, so hopefully it's already taken care of. If your transaction hasn't already been submitted, then I would submit a ticket to our Care team so we can get it resolved for you.
To do so, go in the app to Account > Help > Submit a request
I am guessing it is for Walmart. If you have your Ibotta account linked to Walmart, the receipt is not needed. If nothing was found on your receipt, you may have not selected the offers first.
It should post pretty quickly, but it could take a couple of days. After two days, you will have to submit a request. Go to Account in the app and then Help. Submit a Request is at the top of the screen.
You will probably need to send them a copy of your receipt and a picture of each Ibotta item and UPC. It takes 2-3 days to get a response from Ibotta Care.
For future purchases, if you prefer to submit your receipt yourself, you will have to unlink your Ibotta and Walmart account. Be sure to select your offers before you make a purchase.