Hi and welcome to forum
you will have to contact support about this , asking for giving it back and take the gold you got
this is how to contact them
https://forums.socialpointgames.com/topic/30/how-to-report-game-problems-to-support

@Bala-Rajesh Btw, they may or may not give it back. Ask very nicely to improve your chances. This is also a one time thing as well. If it happens again, they usually don’t refund a second time.

Gold 1000 For EGG VANOSS My SOLD ACCIDENTALLY I

@team-3 Sorry man i don't think you can do anything bout it but be thankful that you didn't sell a meta monster by accident.

Then Back Money My Want I

@team-3 you seriously spent money for Vanoss?

@team-3 Don't lose hope there might be a way.

@team-3 said in accidentally sold the egg how can i get it back (not a bug):

Gold 1000 For EGG VANOSS My SOLD ACCIDENTALLY I

I suggest you send in a ticket to support asking for them to reverse it.