Line an 8-in. square baking pan with microwave-safe plastic wrap, pressing it up sides and leaving a 1-in. overhang. Spray plastic wrap with cooking spray.
Pour citrus juice and granulated sugar into a 6-qt. pot and stir to combine. Clip a candy thermometer to inside of pan.
Cook over medium-high heat, stirring constantly and slowly, until mixture registers 238° (just before the soft-ball stage, when it will harden), about 20 minutes. Add pectin and cook 1 minute more, stirring constantly.
Remove from heat, stir in lemon juice, and immediately pour into prepared pan. Let set until cool and firm, about 1 1/2 hours.
Lift from pan using plastic wrap and cut into 1-in. squares, circles, 3/4- by 1 1/4-in. rectangles, or 3/4- by 2-in. half-moons. Dip in coarse sugar. Store in an airtight container up to 1 week, dipping again right before wrapping if necessary (particularly with the more acidic flavors like lime, lemon, and grapefruit, which tend to get a little weepy).
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Note: Nutritional analysis is per candy.