Hi,
you must :
1) download stone library at https://github.com/STONElibrary/stone_serial;
2) download “instruction for stone uart library” at https://www.stoneitech.com/download/instructions-for-stone-uart-library/ and follow instructions inside this document for Arduino platform, specially at pages 3,4.
3) you need files described in page 3 otherwise Arduino don’t recognize stone commands.
Regards