Login error when coming from AWS - Alexa Integration

I am doing the guides for the alexa integration but struggling right now:

Login attempt failed
Login attempt or request with invalid authentication from ec2-52-214-80-202.eu-west-1.compute.amazonaws.com ( See the log for details.

This comes up when I test the AWS Lambda with the token I created for my user. Locally from the network via postman a basic API call is working with the same token.

I run HA behind a reverse proxy and think that the external (and continuously changing AWS) IPs are blocked. Did not found anything in the logs.

thanks for the help!

Maybe there is a general reverse proxy issue for my setup.
When I am in the LAN, via PiHole DNS the access to the domain is working.
When I am accessing HA via my NGINX PROXY MANAGER (port forwarding from router), I can not sign-in nor access HA via token.

I have the following config:

  use_x_forwarded_for: true
  - ::1
  - router
  - reverse proxy