It works! The problem was old firmware (could not update myself) with new firmware the 'sdk-switch' in the flic-app was turned off, by default -> red dot in the sdk-login-screen turning sdk-switch to on -> green dot in the sdk-login-screen -> login works! thanks @Emil for the directions

@Emil it is a Comodo - Positive SSL multi-domain. I can look up the root, but not right now. If you need it I will have to look it up.

@flic-v not sure exactly what you did but if you set a custom password through the app, this should override the password on the back.