Hello @TheEWL welcome to the community!
What if you pass an object directly to loginWithRedirect
as outlined in this post:
Alternatively, you could use the appState
to achieve a similar result - As noted in the documentation:
If you need to send custom parameters to the Authorization Server, make sure to use the original parameter name.
https://auth0.github.io/auth0-spa-js/interfaces/redirectloginoptions.html#appstate
Hope this helps!