With all honesty, it's not your fault at all that the UGC video is not getting much traction. You did your part and he liked it. But here is the thing. If you ask any graphic designer, they will most likely create more than one design (for a buyer who ordered a single design) just in case the client is not satisfied with a standalone designs. If I were you, I would only create another video free of charge if the client hasn't yet left a review or if the order hasn't been marked as complete. But remember, they can still leave a negative private review so it's still a risk. If the order hasn't been marked as complete yet, it would be in your best interest to create another video for free. All the best.