Stripe integration with 3D Secure - express

Question

I have an Express app that I had successfully tested with tokenisation of payments. As I'm in the UK and will be accepting mainly UK cards, I believe I need to implement 3D Secure handling. I'm really struggling to understand the official documentation - examples are few and far between in my opinion. From the following: https://stripe.com/docs/sources/three-d-secure
I have got Sources working instead of Card payments using tokens. This is step 1. Step 2 requires that I determine if the card supports 3D Secure. I have been doing this client side but am not sure how to handle this subsequently - I have been attempting to send the user for a card payment if 3D Secure is not required. BUT if it is required, do i need to create another Source? And do I do this server or client side? I also cannot get the return_url field to do anything - 3D Secure cards simply fail.
Are there any examples out there that would help me? I am finding the official docs simply tell you roughly what to do with not much in the way of 'how' to do things.
I should add I am using v3 with Elements, NOT Checkout.
Thanks for any help.
edit: the below server-side doesn't seem to do anything:
stripe.sources.create({
amount: 6500,
currency: 'gbp',
type: "three_d_secure",
three_d_secure: {
card: stripeSource,
},
redirect: {
return_url: "http://example.com"
}
})
The documentation states "To allow your customer to verify their identity using 3D Secure, redirect them to the URL provided within theredirect[url] attribute of the Source object."
My source object doesn't contain this field?
edit: This is what I have now. The redirect works, but as soon as I authorize the payment, the card declines:
stripe.customers.create({
email: cust_email,
source: stripeSource
}).then(function(customer){
return stripe.charges.create({
amount: fee,
description: "Client Ref: " + clientref,
currency: "gbp",
customer: customer.id,
metadata: {
'allocation:': allocate
},
receipt_email: cust_email,
source: request.query.source,
})
}
).catch(err => {
console.log(err)
})
stripe.sources.create({
amount: fee,
currency: 'gbp',
type: "three_d_secure",
three_d_secure: {
card: stripeSource,
},
redirect: {
return_url: "http://localhost:8000/charge"
}
}).then(function(test) {
response.redirect(test.redirect.url)
})