First, we need to add the id property to Todo.ts in an Angular app to hold the ID of the Todo item received from the API. So, the updated Todo.ts will look as follows:

export class Todo { 
    id: number; 
    title: string; 
    completed: boolean; 
    constructor(id: number, title: string, completed: 
    boolean) { 
        this.id = id; 
        this.title = title; 
        this.completed = completed; 
    } 
    set isCompleted(value: boolean) { 
        this.completed = value; 
    }  
}  

The constructor takes three arguments: id, title, and completed, and assigns them to the id, title, and completed properties respectively, accessing them using the this keyword. The Todo class also sets an accessor for the completed property.