I havent used a phone scanning app, as I still have on old Sumsung android, but there does seem to be more Apple options available.
For Robbies coin tray, where you'd start would be using a basic program like Tinkercad. Its free, and is surprisingly useful and organic once you get an idea how it thinks. They use it for kids at school, but its easy to learn without getting overly frustrating and is often my go to. Once you get a bit of a handle on it, its the type of program you can just fully exploit all it can do because you can just about fully master it, if that makes sense. Try something simple, all of the bits below I have made from scratch are done just using Tinkercad.
https://www.tinkercad.com/dashboard Draw it up, and save it. The program lets you then "export' it to a printer, making it into an *.stl file which is what you need. Having a cheap digital vernier set is really helpful. Files get stored online, and can be shared.
If there's something you want done, give us some dimensions, or have a rough crack and we can all help 'fix it' online!
The coin tray has curves both ways, but it can be done.
Some examples, Boat parts, model boat keel, I did an MGF drivers mirror adjuster lever thing which looked flashy
