Google has updated its gift card policy in the Google Merchant Center to disallow the sale of gift cards using Buy on Google starting on September 30, 2020. Google said “Beginning September 30, Google will be changing the gift card category policy to prohibit the sale of gift cards on Buy on Google.”
Google added that that Merchant Center products in the gift card category on Buy on Google will be disapproved and will no longer be available to your customers once the policy has been updated.
So if you are currently doing this, Google will disable it around September 30th.
Forum discussion at Twitter.