MongooseError: Operation `therapists.find()` buffering timed out after 10000ms

Question

I have seen this issue published in a few places however I still don't have a solution.

I am using a node server and can connect to my database correctly with a status of 1 for connected.

However when I send requests to the mongodb database, the request pends and times out.

I have tried adding my IP to mongodb, putting my connection in an async function. and also removing mongoose and re installing it.

My structure is like this app client node_modules > mongoose 5.13.14 server node_modules > mongoose 5.13.14

My connection to mongodb is like this.

mongoose.connect(process.env.MONGOOSE_CONNECTION,  { useNewUrlParser: true, useUnifiedTopology: true,  useCreateIndex: true })
.then(res =>{
  console.log("Connected to Database")
}).catch(function (reason) {
  console.log('Unable to connect to the mongodb instance. Error: ', reason);
});

An example of an endpoint that fails is here.

router.get('/therapists', (req, res) => {
    signUpTemplate.find({}, (err, result) => {
        if (err) {
            console.log(err)
        } else {
            res.status(200).send({
                results: result
            })
        }
    })
})

which results in error MongooseError: Operation therapists.find() buffering timed out after 10000ms

Can someone help me please as I am really not sure what the solution is. Thank you!