Firebase functions not registering document which definitely exists

I am trying to create a firebase function HTTP endpoint which will allow the posting of a user ID and return if the user exists in the database or not.

Structure of my database:

User ID = document ID in users collection

What I have tried

I created the following code, which would always return "User does not exist!" even when providing an existing user ID:

const functions = require("firebase-functions");
const admin = require("firebase-admin");
admin.initializeApp();

exports.userExists = functions.https.onRequest((request, response) => {
  if (request.method !== "POST") {
    return response.status(400).send("Please send a POST request");
  } else {
    const userRef = admin.firestore().collection("users").doc(request.body.userID);
    userRef.get().then((doc) => {
      functions.logger.info(doc.data());
      if (doc.exists) {
        response.status(200).send("User Exists!");
      } else {
        response.status(200).send("User does not exist!");
      }
    }).catch((err) => {
      response.status(500).send(err);
    });
  }
});

I even tried hardcoding the user ID into the function, with no luck either:

const functions = require("firebase-functions");
const admin = require("firebase-admin");
admin.initializeApp();

exports.userExists = functions.https.onRequest((request, response) => {
  if (request.method !== "POST") {
    return response.status(400).send("Please send a POST request");
  } else {
    const userRef = admin.firestore().collection("users").doc("DGxyfSrLnzLTp3Adzmm7VL6sOZz2");
    userRef.get().then((doc) => {
      functions.logger.info(doc.data());
      if (doc.exists) {
        response.status(200).send("User Exists!");
      } else {
        response.status(200).send("User does not exist!");
      }
    }).catch((err) => {
      response.status(500).send(err);
    });
  }
});

Code for calling the function, and output:

import requests

data = { "userID": "DGxyfSrLnzLTp3Adzmm7VL6sOZz2" }
r = requests.post("https://{domain_hidden}.cloudfunctions.net/userExists", data)

print(data["userID"])
print(r.status_code)
print(r.headers)
print(r.text)

I am completely stumped and can only assume now that I am missing something simple, so reaching out here for advice. Thanks.

EDIT -- as requested the code used to create new users

I see now as suggested by @Dharmaraj that the user's IDs are in Italics, meaning they do not actually exist. I actually created the user Docs by creating docs in a user sub collection called plants. The code is as follows:

const plant = await addDoc(collection(firestore, "users", user.uid, "plants"), {
  name: plantName
});

Do I need to explicitly create a user document before creating items in subcollections?