great job with the anti-scooter vtriol... except y'all the idiots, not the OP, who don't know the difference between a moped and a scooter. the onyx is an electric moped. not a scooter.
they do have some dumb cheap generic Chinese scooter brake setups , but they work well and are real similar to ones folks adapt to their mopeds whenever using disc. In fact I think it's even the exact same one treats sells for the EBR's. https://www.treatland.tv/GOLD-disc-brake-caliper-p/gold-disc-brake-caliper.htm
Further, the reviews on that product mention THIS EXACT PROBLEM
sounds like it's just a chore, but doable. can't remember doing it myself but I've done similar ones, maybe that same one; you have to compress the piston all the way back and I think you have to pull the side to side play adjuster (slide pin that lets the caliper move outward from the mounts) all the way out, then you kinda put the pad in the spring and then wiggle the pads in while compressing the spring clips.
Side note: many people have found that the onyx mounting tab for the caliper puts it too far out on the rotor so it only clamps the outermost edge. you can maybe shave the mount or redrill it so the pads sit more squarely on the disc rotor.