Motorcycle Questions? Ask a Mechanic.
Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, please check/re-confirm correct polarity.
And if have not been tried; inspect the battery & ground lines and/or check/clean the battery cables + terminals as a preliminary consideration. Better yet, have the battery externally charged and then LOAD TESTed (even if new and just for the purpose of eliminating it as a suspect).
Still, re-check the starter relay. Carefully but quickly/momentarily jump the two (2) big terminals. This is a bypass of the starter relay to enable the starter motor to spin:
Please post back results / observations of the above once tried.