Invalid csrf token even though it exists

Hello, I’m having a hard time understanding why I’m getting the error:

invalid CSRF (Cross Site Request Forgery) token, make sure all requests include a valid '_csrf_token' param or 'x-csrf-token' header

Even though the form has a _csrf_token field with the value of Plug.CSRFProtection.get_csrf_token().

I tried setting it directly in the form like:
<input type="hidden" name="_csrf_token" value="<%= @token %>">

And using the form_for function which auto generates the csrf token.

In both cases, the token is there, however, when I post the form, I always get the Plug.CSRFProtection.InvalidCSRFTokenError exception stating that a valid token should be present.

For extra context, my pipeline is:

pipeline :browser do
  plug :accepts, ["html"]
  plug :fetch_session
  plug :fetch_flash
  plug :protect_from_forgery
  plug :put_secure_browser_headers
  plug MyApp.Plugs.SubdomainPlug
end

Any help would be appreciated.

EDIT
I’m using the following:
phoenix 1.4.9
phoenix_html 2.13.3
plug 1.8.2