The pharmacy may be having trouble because they need your vet's DEA number to process the coupon for your pet's prescription. They can call your vet to obtain the DEA number, or it may already be on the script.
In the pharmacy's system, human prescriptions require a number called an NPI to identify the doctor who prescribed the medication. Pet prescriptions may use a DEA number instead, since vets do not have have NPI numbers (just in case the pharmacist tries to tell you differently).
Also, while a DEA number is typically only needed for controlled substances when it comes to human prescriptions, it is the only number that will work for pet prescriptions.
Once the pharmacist has your prescriber's DEA number, they should be able to process the coupon without any problems.
If the pharmacist does continue to have trouble, the quickest way to resolve any issue is to ask the pharmacist to call the help number on the coupon while you're in the pharmacy. Someone from the help line can speak directly to the pharmacist for you to clear up the problem while you're there. If the help line isn't available, or if they don't resolve the issue, you can always get in touch with us here and we can generally work with the coupon provider to resolve any misunderstandings.