[next-auth][error][CLIENT_FETCH_ERROR] "Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON" (SOLVED)

[Salman-165324]

After adding the next auth and Google provider. I was getting this error on the client side:
[next-auth][error][CLIENT_FETCH_ERROR] "Unexpected token '<', "<!DOCTYPE "... is not valid JSON"

And getting the following error on the server side:
TypeError: cookie is not iterable

[Salman-165324]

I did the following things. And it has solved my issues.

Deleted the [...nextauth] folder. And created again.
updated my nodejs to the latest LTS version.
I think the second one worked the magic.