Alexa Skill manual configuration issues with Balena HA instance

Hi there, I’m new to HA and I’ve been trying to integrate a Balena HA instance with Alexa manually following this tutorial:

I’ve created the Lambda in AWS and the dev skill in the Alexa developer console, the Lambda function passes the test. The problem comes up when I try to link my home assistant acount to the Dev skill in the Alexa app, when I try to enter my credentials I get the error: “Invalid Redirect URL”.
What can I be doing wrong? Is this something related to HA being deployed with Balena?

Thanks in advance