Biofeedback devices are used commonly by physiotherapists for the rehabilitation treatment of a wide range of neuromuscular and musculoskeletal problems. Physiotherapy centres in India purchase imported biofeedback units which come packed with multiple features for electrostimulation, EMG biofeedback, pressure biofeedback, etc. This makes the devices multi-purpose and expensive. The cost of such devices and their complex usability limit their usage to therapy centres and trained therapists. In this design project, we looked into the use of biofeedback for Brachial Plexus Injury (BPI) rehabilitation. Biofeedback is used primarily for muscle re-education after nerve transfer surgery in BPI treatment. Considering the ecosystem of a govt physiotherapy centre that specialises in BPI rehabilitation, we identified the challenges they face in providing the best results to their BPI patients. This design project presents a cost-effective sEMG biofeedback solution that is simple to use and specific to BPI rehabilitation. Eliminating use of dedicated hardware for displaying biofeedback signals and using a smartphone app instead reduces the cost of the system. The solution includes sEMG sensor units along with an accompanying mobile application that can be used by both physiotherapists and BPI patients. Expert evaluation of the design of the system and the mobile app was carried out at the end of the project.