Grandfathering from paid to subscription when original purchase was through a promo code

[israeltabadidev]

Hi, I have an app which was converted from paid to subscription.
I have several users who were given a promo code for the paid app before it was changed to subscription model who are complaining that it didn't transition for them.
Is this a known issue for users who used a promo code? Do they not have original receipts?