Hello Gema,
usally Prompt is only used to show the hint its not saving data whatever present in your variable property that is only stored in the database not a prompt
EDIT:

Please read the info for the prompt so here its clear whatever present in prompt its just hint not actually value
if you want to set that as hard code then you can passed that value on the onready/on initialize action (map that value to the variable which is assign to the variable property )
what ever you passed on the variable that is only able to stored in the database
Thanks and Regards,
Akshay Deshpande