Place the chicken thighs in the slow cooker. Add the apple cider, chicken broth, onion, carrots, celery, and thyme. Season with salt and pepper.
Cover and cook on low for 6 hours until the chicken is tender.
Shred the chicken directly in the slow cooker with two forks.
In a mixing bowl, stir together the flour, baking powder, milk, and melted butter until a soft dough forms.
Drop spoonfuls of the dough over the hot chicken mixture.
Cover and cook on high for 1 hour until the dumplings are firm and cooked through.