Is it because customers are placing multiple orders under the same offer?

At the Product Transactions screen:

Compare the Promotion Codes and PO numbers. If the customer has multiple Gratis order lines for the same promo code and PO Number this is not due to multiple orders. Testing/Troubleshooting is needed.

At Order Entry:

Place a test order using the promotion code/choice in question to confirm that the issue is still occurring. No need to post the order at this point.

Check SVCPRM-Premiums for the test account. Were multiple premium sets generated for the same order number? Go to Promotion Offers. Customize both frames to display the Premium Set column.

• Is there a premium set on the Offer and the Choice? If so, do both premium sets contain the same item? 

• Is there a single Premium Item on the Offer? 

• Is the “Fulfill once per recipient” box on the Premium Set checked?

If an item is being generated in more than once place in the marketing setup, whether it’s a Premium Set on the Offer and on the Choice, or a Premium Item on the Offer and a Premium Set on the Choice, we recommend that the potential for duplication be removed. The best way is to set up Premium Sets holding PRO or CIR items (and soon AMB) on the Choice level only. List codes aren’t a concern, as the customer’s email cannot be added to a list more than once.  The “Fulfill once per recipient” box should almost always be checked. Please let me know if there is a situation where this box being checked is causing an issue.

If the test order does not generate duplicate items, check the last updated date on the Offer and Choices to see if anyone has made changes recently and/or compare the setup in Production to the setup in Train or Stage. Sometimes the affiliate changes the setup and resolves the issue before it comes to our attention.

If the item is only being generated once via the marketing setup, and the “Fulfill once per recipient” box is checked and duplicate premiums continue to be generated we are most like looking at a bug and the Advantage team will need to do additional research.

See Advantage Help for more information

https://help.advantagecs.com/manual/en-us/2016/CPN/premiums