Thanks for reaching out, that is a great question. Also, I see this is your first post here in the Shopify Community - you are very welcome! I understand you are wondering if you can set an expiry date for gift cards, and have it always be the end of the year of expiry.
You can indeed set expiry dates on gift cards. This can be done when manually issuing a gift card, or when a customer purchases a gift card product. When you are issuing the gift card you will see an 'Expiration Date' section where you can choose the exact expiry date. After the gift card has been created, you can also change the expiration date by clicking into the gift card, and then clicking the link under where it says 'Expiration date'.
You can also set your gift cards to expire a certain amount of time after they’ve been purchased by a customer. This can be done by navigating to Settings > Gift Cards and then setting a time frame in days, months or years.
Depending on your region's laws surrounding gift cards, you might not be allowed to add an expiry date or to limit the way in which the gift card is used, so I would encourage you to double check this before doing so.
You asked if you can set the expiration date to 3 years, but always expire on Dec 31st. This is not something that you can choose when issuing a gift card via the Shopify admin, as you will only be presented with a selector to choose a specific date, or an X amount of days/months/years time frame. We have more information on selling gift cards on Shopify here.
It may be possible to achieve this by using an app, or with some sort of custom coding solution, however I am not a developer myself so I cannot say for sure. Feel free to browse the various gift card apps in the Shopify App store here. If you find an app you like, feel free to contact the developers and ask them about your request - they may be able to advise you on that! I would suggest checking out this blog post here about gift cards which outlines how you can incorporate gift cards into your business, and it also has a section recommending some third-party gift card apps as mentioned above. You could also consider hiring a Shopify Expert to help you find some sort of custom solution.
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