Monetary incentives for increasing participant retention rates in the ComEx Pain feasibility trial

1. To evaluate the effectiveness of an unconditional €25 gift voucher incentive versus no monetary incentive for increasing participant retention at the primary outcome follow-up timepoint in the ComEx Pain randomised feasibility trial
2. To evaluate the cost-effectiveness of the monetary incentive strategy.
3. To undertake a process evaluation to explore the ethics, acceptability, and future implementation of the monetary incentive strategy in the full feasibility trial.