I have seen this a few times. You can try a few things.
First, select the offer to see the details. Sometimes you can select the offer there.
If that doesn't work, try restarting your phone.
If this still doesn't work, I would take a screenshot of the offer in case you have to submit a request. If you purchased the item but didn't get credit, I would include the screenshot in your request for credit, along with pictures of your receipt.