How to set cursor position to the end of segement location in a fetch requst?

Question

I am currently sending a post request to a Google Document to insert some text. This is how I do it:

const updateDoc = async (token, ID, requests) => {
const postLinkDocs = `https://docs.googleapis.com/v1/documents/${ID}:batchUpdate`;
try {
    await fetch(postLinkDocs, {
        method: 'POST',
        headers: {
            Authorization: 'Bearer ' + token,
            'Content-Type': 'application/json',
        },
        body: JSON.stringify({
            requests: requests,
        }),
    });
} catch (error) {
    console.log('Batch update error:', error);
    return false;
}};

Where my request looks like this:

const requests = {
                    insertText: {
                        text: word + ' ', // ' ' is used to add space
                        endOfSegmentLocation: {},
                    },
                };

Where the text I am sending is from a Speach to Text API. It gets the words right on the docs, always appending to the previous text |This was the first text and then it came the second But my cursor doesn't update with it (the | represents the cursor postion, being stuck at the start). I also checked in Google Apps Script for its value and is always null.

const doc = DocumentApp.openById(docID);
const body = doc.getBody();
const cursor = doc.getCursor(); 
console.log(cursor) <- returned null even though cursor is displayed at the begging of the docs

Is there a way to update its position inside the request or in GAS?