Google assistant doesn't find entities after setup

I set up google_assistant integration based on the instructions provided in the description of the integration.
When try to add a new device in my Google Home app, there is my newly created [test] hass app and when I click on it, I have to authenticate using my HA username and password. Afterwards I’m redirected back to the Google Home app, but neither is it added to the Linked Services nor is there any entity added. The configuration:

  project_id: "hass-abcxyz"
  service_account: !include hass-123456.json
  report_state: true
  expose_by_default: true
    - switch
    - light

The endpoint https://public.hass.domain/long_secure_token/api/google_assistant is accessible to Google and redirects internally to my local https://local_ha/api/google_assistant using nginx proxy_pass via a VPN tunnel.
Both public.hass.domain and local_ha have proper letsencrypt certificates installed.

Any idea where to debug it? I didn’t see any log entries in HA, yet. Thanks for any hint.

What I’ve noticed: I don’t see any requests from Google going to the api/google_assistant endpoint in nginx’ access.log. I’d assume that the assistant would try to gather entity data after authentication.

Fixed it. In nginx the trailing / always makes trouble.

location /secure_string/auth/token/ {

won’t work. One has to do it this way:

location /secure_string/auth/ {

As a note, disabling buffering in nginx will make actions quite fast:

proxy_buffering off;