Good morning, I wonder why after I updated my phone the application widget did not work again.
you are going to need to be more specific then that if you expect anyone to be able to help.
BLYNK has a lot of widgets, and you say
What was the cause of it not working the first time?
Code? Device?
my cell phone is Moto Z Play, I upgraded to android 8 and when I started device after the update the widget I had from a project “disappeared” and asks me to put it back again by spending 100 more energy
So… you are referring to a Phone’s widget of a Blynk Shortcut (clarity matters) 
I don’t think Blynk can control whether or not your phone OS upgrade wipes out Phone widgets or not.
Just re-enable it… 100 energy works out to a few pennies at most.