While this isn't the proper forum for Grand Caravan questions, I'll respond anyway.
Do you get an indication that the vehicle acknowledges the request to open the liftgate? If so, have you tried to manually assist it in opening, or opening the liftgate manually? If it will open with your help, or manually, but will not stay open, the issue is likely that the gas strut/struts that assists with opening and keeping the liftgate open is/are likely worn and need to be replaced. Replacing them should get the automatic feature working again.