I extruded a pocket to include (2) 10mm x 60mm x 3mm magnets. The gcode and the 3MF include a pause for the magnets to be added. I strongly suggest using CA glue with an activator when installing the magnets since they will interact with each other and a hardened nozzle.
When I saw that equivalent magnet cases online were selling for as much as I paid for a fire stick, then I decided to make my own. My supports are experimental and depending on your TPU you may have some post printing cleanup of the interface material. I printed at 101% in the gcode and 3mf, keeping the original scale for those that wanted it. 101% seemed to work best for me.
The author remixed this model.
Added (2) 10mm x 60mm rare earth magnets to make this a case that could stick to a metal cabinet door.