solenoid valve for that jack is likely not receiving 12V to open, or else solenoid is bad and not opening when it does get 12V.
You can pull the plug to the solenoid & check for 12V when manually activated. If that shows 12V then the valve isn't opening to allow fluid to flow. You can get it rebuilt by HWH or get a new one. You can check the inop solenoid valve by swapping it w/a known good jack's solenoid & verify the know good one is now inop & the bad one works.
Baja-tested '08 2-slide 36'
Alpine: The Ultimate DIY'er Project