can’t connect valve to pump

novice cyclist here-
I rented a bike for a few days as i’m visiting family so not using my regular bike.

I’m trying to check air pressure and can’t seem to connect to the presta properly on the rear- it’s not locking in properly regardless of how i try to do it, with air coming out as soon as i try to pump.

No issues on the front but it’s different looking / shaped valves so i’m assuming different inner tubes.

I know i’m not doing something properly but can’t seem to figure out what it is…

any idea what i’m doing wrong?
thank you so much and happy holidays!