Stripe No such customer (Express Connected Account)

I'm trying to allow users to create one-off invoices after they have onboarded to the platform via an Express account.

I have a Node route set up to create and send an invoice.

I'm getting the error

 StripeInvalidRequestError: No such customer: 'cus_I3Xra0juO9x2Iu'

However the customer does exist in the user's connect account.

The route is below

app.post('/api/new_invoice', async (req, res) => {
        try {
            const { customer, deliverables, amount, payableBy } = req.body

            const product = await stripe.products.create({
                name: deliverables,
            })

            const price = await stripe.prices.create({
                unit_amount: amount,
                currency: 'aud',
                product: product.id,
            })

            const invoiceItem = await stripe.invoiceItems.create({
                customer,
                price: price.id,
            })

            const stripeInvoice = await stripe.invoices.create(
                {
                    customer,
                    collection_method: 'send_invoice',
                    days_until_due: 30,
                    invoiceItem,
                },
                {
                    stripeAccount: req.user.stripeAcct,
                }
            )

            const invoice = await new Invoice({
                customer,
                deliverables,
                amount,
                paid: false,
                issueDate: Date.now(),
                payableBy,
                _user: req.user.id,
            }).save()
            res.send(invoice.data)
            console.log(invoiceItem, stripeInvoice)
        } catch (err) {
            console.log(err)
            res.status(400)
            res.send({ error: err })
            return
        }
    })

From what I understand adding a second object to stripe.invoices.create with the connect account's id then it should look into their Stripe account for the customer?

Thanks in advance