Study 1: Identifying and meeting patients' needs Design: Focus groups with individuals with chronic pain and health care professionals. Aim: To identify participant's needs and utilise user input to match the treatment content and design (prototype 1.0) to needs. Sample: People with chronic pain (two focus groups, n=6-8 per group), health care professionals (HCPs) (e.g., psychologists, psychotherapists trained in cognitive behavioural therapy (CBT)) (one focus group, n=6-8) will be recruited from primary care facilities in the region of Kalmar. Data collection: Focus groups will follow a semi-structured guide and be audio- and video-taped. Field notes will furthermore provide insights into relevant cues and observations given by participants. Outcome: Intervention prototype 2.0 Time plan: Autumn/winter 2021.

Study 3: Feasibility, acceptability, preliminary efficacy, and individual change processes Design: Piloting and optimising the treatment in an iterative process with 4-6 smaller cohorts; user input from each optimisation 'sprint' will be integrated and tested in the subsequent cohort/ sprint; single-case experimental design (SCED) method with randomised baseline length, pre- post- and FU-assessment and post-treatment user interviews. Aim: To evaluate the feasibility and acceptability, the preliminary efficacy, and individual change processes of the digital behavioural health treatment within the 1177 web-platform. Sample: People with chronic pain (n=10 per sprint; total of n=60) will be recruited from primary care facilities in the region of Kalmar; the feasibility and acceptability will also be evaluated in treating HCPs (note: one HCP might treat multiple patients at the same time, and also take place in several sprints), who are therefore also considered participants. Data collection: feasibility/ acceptability: semi-structured debriefing interviews of subjective experience combined with objective measures such as drop-out rate, adherence, system-generated technical use e.g. number of log-in time points, number of modules completed; preliminary efficacy: Pre-, post- 3- and 6-month FU-assessment of self-reports on patients' well-being, data of n=60 patients accumulated across all sprints as the treatment remains functionally constant across all optimisation studies; individual change processes: Lunch and evening reports of well-being at least four times per week over the course of the 6-week treatment using a digital diary, also comparing to the baseline and post-treatment diary assessments. Time plan: 2022.

Study 4: RCT enhanced with SCED evaluating the (cost-) effectiveness and maintenance of change Design: Two-armed RCT enhanced with randomized baseline length SCED method comparing the digital behavioural health treatment to primary care treatment as usual (TAU). Aims: To evaluate the clinical effectiveness of the treatment on behavioural health outcomes, and the cost-effectiveness of the treatment in comparison to TAU. Sample: Patients (n=360, n=180 per group) will be recruited from pain clinics and primary care facilities in the region of Kalmar and potentially other regions (e.g., Östergötland, Jönköping, Stockholm, Uppsala, Örebro). Data collection: Self-report questionnaires will be completed over pre-, post- FU-assessments. Furthermore, the digital diary information on daily well-being will be collected at all assessment time points and over the course of the intervention, in both treatment arms. To determine the cost-effectiveness, information from registers on sick leave, medication, and health care consumption will be used . Time plan: 2023-2024.

Study 2 (pre-Implementation) and study 5 (post-implementation): business model, determinants, and lessons-learned Design: Qualitative study using interviews with stakeholders; deductive analysis of qualitative data mapped on the consolidated framework for implementation research. Aim: Identify barriers and facilitators for the prospective implementation of the treatment and prepare the implementation process using a business model canvas (at baseline, study 2); review the actual use and implementation process at follow-up to present lessons learned (at follow-up, study 5). Sample: Various stakeholders identified via snowball-sampling (e.g., development team and facilitators of 1177 web platform at region Kalmar, health care professionals, health care managers, municipality representatives). Interviews will be conducted until data satisfaction is achieved. Data collection: An initial version of a business model canvas will be discussed with the development team and health care managers. Furthermore, potential barriers and facilitators of prospective use will be identified at baseline via a semi-structured interview with the stakeholders. The practical use and implementation status after the treatment is released to the market (here also referred to as follow-up (FU)) will be described using semi-structured interviews to understand the process retrospectively and present lessons learned. Time plan: baseline autumn 2021, FU in autumn 2024 (after RCT, treatment release to other regions).