"To choose the sum" means to select or decide on the total amount or quantity of something. It refers to the act of making a decision about how much of something should be added or combined together.
Sentences with «to choose the sum»
Variable minimum premium for plan 1: Depends on chosen sum assured. (life.indiainsured.com)
One has to be very careful at the time of choosing a sum insured. (policybazaar.com)
Some plans give you the option of choosing your sum assured. (business-standard.com)