In a medium saucepan, combine water and butter. Bring to a simmer over medium heat until the butter is melted.
In a separate bowl, whisk together the flour, sugar, baking powder, and salt.
Once the butter is melted in the saucepan, remove from heat and add the flour mixture. Stir vigorously until a dough forms and pulls away from the sides of the pan.
Allow the dough to cool slightly (around 5 minutes), then transfer to a piping bag fitted with a large star tip.
Preheat your air fryer to 375°F (190°C) for 5 minutes.
Pipe small bite-sized churros (around 1 inch long) directly into the air fryer basket, spacing them apart. Spray lightly with cooking spray.
Air fry the churro bites for 8-10 minutes or until golden brown, flipping them halfway through for even cooking.
While the churro bites are cooking, mix 1/4 cup sugar and cinnamon in a shallow bowl.
Once cooked, remove the churro bites from the air fryer and immediately toss them in the cinnamon sugar mixture until evenly coated.
Notes
For best results, pipe churros evenly and do not overcrowd the air fryer basket.