Why do I get an absolute URL error in xero oauth for a valid URL?

I am using xero-node for javascript development but I am getting an error when I try and create the xero client. I call this code.

const consentUrl = await xero.buildConsentUrl()

I create the xero client with this code:

xero = new XeroClient({
  clientId: clientId,
  clientSecret: clientSecret,
  redirectUris: URL_REDIRECTS,
  scopes: ['openid', 'profile', 'projects']
  //state: 'not_currently_used', // custom params (optional)
  //httpTimeout: 3000 // ms (optional)
})

This throws the error:
index-C0C0EiKl.js:117 Uncaught (in promise) TypeError: only valid absolute URLs can be requested.

Looking at the debug I see it gets thrown in this code.

try {
    t = new DX1(e.url),  //thrown here
    delete e.url,
    RX1(/^(https?:)$/.test(t.protocol))
} catch {
    throw new TypeError("only valid absolute URLs can be requested")
}

The e.url that it is using when it calls this code is https://identity.xero.com/.well-known/openid-configuration. When I put this URL in my browser it returns valid configuration data. So I have no idea why this URL is unacceptable.

I’d appreciate any help from a xero expert here please.