Aggregate return empty array with custom variable - mongodb

Question

Here is a link to understand the structure : https://mongoplayground.net/p/TUsBjiboKLk
I'm basically looking for the communities that the user is following which work just fine in mongoplayground.
But replacing the "userId1" with a custom javascript variable is not working.
pipeline: [
{
$match: {
userId: "userId1", // <================
$expr: {
$eq: [
"$userId",
"$$userId"
],
},
},
},
],
pipeline: [
{
$match: {
userId: myCustomVarible, // <================
$expr: {
$eq: [
"$userId",
"$$userId"
],
},
},
},
],
Here is the full code for further explanation:
app.get("/communities/following", (req, res) => {
const userId = req.query.userId;
Community.aggregate(
[
{
$lookup: {
from: "follows",
localField: "communityId",
foreignField: "communityId",
as: "follows",
},
},
{
$unwind: "$follows",
},
{
$lookup: {
from: "users",
let: {
userId: "$follows.userId",
},
pipeline: [
{
$match: {
userId: userId,
$expr: {
$eq: ["$userId", "$$userId"],
},
},
},
],
as: "users",
},
},
{
$unwind: "$users",
},
{
$project: {
name: 1,
avatar: 1,
},
},
],
(err, data) => {
if (err) res.status(500).send(err);
else res.status(201).send(data);
}
);
});
If i replace const userId = req.query.userId; width const userId = "myUserId"; it's working

Answer 1

Ok, i found the problem, i was testing this using :
http://localhost:9000/communities/following?userId="7arvEbQx3wVttqnbwmOionRsPBz1"
where it should be without the quotes
http://localhost:9000/communities/following?userId=7arvEbQx3wVttqnbwmOionRsPBz1