The gift card balance page shows a tag.
Where can I find this string to fix it?
The reason you’re seeing the raw HTML tag like instead of the styled amount on your gift card page is because the variable you’re using is printing the code as plain text rather than actually rendering it as HTML.
You’ll want to check the line in your Liquid file that outputs the amount, something like:
Amount: {{ gift_card.balance | money }}
Just output the amount normally with {{ gift_card.balance | money }} and let your theme’s CSS apply the styling.