Typescript: How can I extract the value from JSON objects inside an array with changing property names?

I’m new to typescript and would like to extract the value from JSON objects inside an array with changing property names.

My (simplified) code is as follows:

const data = [
              { names: { "1,2": "Matthew" },
              { names: { "2,3": "Marcus", "3,4": "Bill" }},
              { names: { "4,5": "Joana", "5,6": "Bob" }
             ];

const key = "1,2";

const name = data[0].names[key]; // Results in an error message (see below)
const name = data[0].names["1,2"]; // Works but not dynamic

My goal is to extract each value (e.g. “Matthew”, “Marcus”, etc.).

However, I get the following error message:

Type ‘{ names: { “1,2”: string; “2,3”?: undefined; “3,4”?: undefined; “4,5”?: undefined; “5,6”?: undefined; }; }’ is not assignable to type ‘string’

How can I solve this error?

Thanks a lot for your help!