Digitally delivered cognitive behavioral therapy for insomnia (CBT-I) for patients with chronic pain and insomnia (The Back2Sleep Trial): study protocol for a randomized controlled trial. - Olsen, Maria Louise Stage; Thorlund, Jonas Bloch; Zachariae, Robert; Vach, Werner; Bendix, Laila; Jespersen, Julie; Kidmose, Preben; Parsons, Christine; Kidholm, Kristian; Vægter, Henrik Bjarke (Trials, 2025)