Combine the sugar, lime juice and 2/3 cup regular water in a medium microwave-safe bowl. Microwave in 30-second intervals, stirring in between each, until the sugar is dissolved, about 2 minutes. Add the seltzer water to the syrup mixture, sprinkle the gelatin on top and leave it to bloom for 5 minutes.
Microwave the bloomed gelatin mixture until dissolved, about 30 seconds. Sir in the tequila and orange liqueur. Divide the mixture among twelve 2-ounce glasses. Refrigerate until set, at least 3 hours.
Before serving, garnish each shot with a small pinch of flaky sea salt and a lime wedge.
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