core: Error: Unable to Register Application with android app

First ever issue on github, hope I am formatting this the right way.

Home Assistant release with the issue:

Home Assistant 0.103.4

Last working Home Assistant release (if known): None

Operating environment (Hass.io/Docker/Windows/etc.):

Operating on a synology within docker container. homeassistant-home-assistant image. Synology is attached to the network. Port 80/443/8123 are forwarded

Integration:

https://www.home-assistant.io/integrations/mobile_app#apps

Description of problem: When I manually try to reach my home assistant through the android app (home assistant), I reach the inlogscreen. when I try to log in i get the notification: Unable to Register Application Please check to ensure you have the mobile_app integration enabled on your home assistant instance.

Problem-relevant configuration.yaml entries and (fill out even if it seems unimportant):

# Configure a default setup of Home Assistant (frontend, api, etc)
default_config:

# Uncomment this if you are using SSL/TLS, running in Docker container, etc.
 https:
   base_url: https://www.domain.nl

# Text to speech
tts:
  - platform: google_translate

homeassistant:
  latitude: xxxx.xxxxx
  longitude: x.xxxxxxx
  elevation: 2
  unit_system: metric
  time_zone: Europe/xxxxx
  name: Home
  customize: !include customize.yaml

group: !include groups.yaml
automation: !include automations.yaml
script: !include scripts.yaml
scene: !include scenes.yaml

frontend:
  themes: !include themes.yaml

influxdb:
  host: xxx.xxx.xxx.xx
  
mqtt:
  broker: !secret mqtt_url
  port: !secret mqtt_port
  client_id: home-assistant
  discovery: true
  discovery_prefix: homeassistant
    
yeelight:
  devices:
    xxx.xxx.xxx.xxx:
      name: Overloop

panel_iframe:
  configurator:
    title: Configurator
    icon: mdi:wrench
    url: 'http://xxx.xxx.xxx.xx:xxxx'

hacs:
  token: ***********************************************

sensor: !include sensor.yaml