Put quotation marks at the source and format of the file.

[Jhon Toledo]

mappings:
  stoptimes:
    sources:
      - [/data/STOP_TIMES.csv~csv]

rml:source /data/STOP_TIMES; -------------------> rml:source "/data/STOP_TIMES.csv";

[LuisLopezPi]

I think I've fixed it