Why don't the back jacks go up when I press hitch height on the control pad

ask your RV center what to do ,?

Model: 6.49-1 18.57-1
Travel height: 7ft 3in 8ft 7in not sure why two heights maybe second height is when expanded ?
https://www.caravancampingsales.com.au/editorial/details/jayco-expanda-20433/

You will need to take the trailer to a CAT scale at a truck stop. The trailer should have a hitch, you just need to figure out what size receiver ball you need; 2" or 2-5/8". Each ball has a specific limit. That alone should give you an idea of the weight. At the CAT scale, there are several scale pads, put the axles on one scale and the tongue/jack stands on another. Your total will be from both scales but this will also give you an idea about the weight distribution.

The control valves for each jack are no longer functioning. Time to replace them.

These guys usually have that kind of stuff but you can also do a google search for RV Leveling Jack Control Board for other options (like ebay)
http://rvcomponents.visonerv.com/cgi-bin/f/levelingsystemcontrollers.pl

Take it in to the service department where you purchased it. Sounds like you have picked up on of those stow away hitch hikers that hide out in the retractables, like those airliners have had happen. Just a little humor. Take it to the service department...just like the message says....sort of.

Take off the top cap and there should be access for a hand crank that should have come with the trailor

The jack system is wired through various safety apertures and all must be in the proper setting for the system to work. Many require the emergency parking brake to be set, the vehicle must be in park and I have even seen one system that the driver must be in their seat with their safety belt on before that jacks would retract. The last vehicle I repaired with this issue I found that on the dash the vehicle indicated that it was in park but the neutral switch located on the transmission had not properly locked into park. Have you visually inspected the jacks to verify their position. There are times that the jacks will retract but due to low fluid level the alarm remains activated showing that the jacks are down. With these systems, in most cases, the jacks retracting is basically a release valve being activated and springs pulling the jacks back up into the retracted position.

Bleed back right corner jack loosen fitting on jack till unit is level tighten