Offer shows in red when trying to redescribe a book

I have tried to redescribe some books and for some reason it won’t let me with the word “offer” appearing in red, and at the bottom within a red rectangle the phrase " Handling Time : The value provided is lower than the minimum allowed: 1.
Handling Time : Value must be greater than or equal to 1.""
As the book in question has a value of £15 I am at a loss to understand the problem.
Has anyone else have experienced this?