It is a service message definition you need to have compiled in your workspace in order to be able to call it.
Checking service is advertised under /erc_aruco_score. It is defined in the erc_aruco_checker package (available here). The request message type is of ErcAruco.
It is defined in the erc_aruco_msg package as 14 float32 arrays of 3 numbers, which correspond to 14 tag positions (tags from 1 to 14). On the scene. The returned type is a single float32 value with your obtained score. The tag placed inside the box on the panel is not taken into account.