There are several reasons this might happen. 
1. The email address may be entered incorrectly. Please correct it. 
2. Your offer may have reached its cap and no more offers are being sent out. You can increase the claim limit. 
3. Your offer email may be stuck in the customer’s SPAM folder. Please ask the customer to check and mark your offers email as not spam.

4. Please make sure that the Clover Marketing Allowed flag is set properly for the customer.