Modern Vespa

Went on a ride on Sat and it was all good. I stopped for some errands and since then, I am unable to shift to first gear. It won't snap in the slot as seen on picture.

I tried to loosen up the gear cables and even take them off to switch at the selector while spinning the wheel. Seems like something stuck inside on the first gear. 2nd and 3rd gear are working fine. Any thought?

ok, so you have ruled out that the problem is caused by the cabelling.

then there are two options the selector rod or the gears.

if you cannot move the selector rod that means you cannot reach the scews underneat to remove it, meaning you have no other option then to split the cases.

you can drop the engine and check the clutch and the primary but highly unlikely they are causing the problem...

you can try to remove the wheel and give the driveshaft a few smacks with a hammer to see if anything might pop into place, but thats a long shot....