The Customer Account Dr. entry should not come. It again has to hit the Sales Promo Acc only.
I didn't think it is a right idea/way to include excise amount to Sales Promo Acc for free of charge sales.
You need to get those duty amount different to "Duty adjustment a/c". B'coz you are liable to pay those duty to Govt, until you have proper exemption for paying those duty. Which you will not be able to differentiate, if take to Sales Promo a/c. For hint on this, refer my suggestion in following thread,
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Alternatively, you can follow, what is been suggested by Lakshmipathi Sir.
But in my opinion, you should have discussion with your Finance for this.
Regards, JP