Corrosion on the starter button contacts.
Open the switch spray it with wd40 and operate it with ignition of 4 or 5 time and then try it. If that does not solve it remove the button and clean the contacts with fine emery paper, reassemble and off you go
Open the switch spray it with wd40 and operate it with ignition of 4 or 5 time and then try it. If that does not solve it remove the button and clean the contacts with fine emery paper, reassemble and off you go