Login results in Connection error

Not sure, if this is the right forum:

I have installed the IOS App V1.1.1 and Home Assistant 0.84.6.
I enter the external ip of my HA (https://asbvdec.myfritz.net: it’s the Fritzbox DNS Name with port 443, which is forwarded to my nginx reverse proxy on the same RaspberryPi) and the password)
Question: Password for which user?
When I click on Ready, I get the following error (which says connection error - wrong password:

But when I click on OK, HA opens and shows a failing login attempt from

When I close the App and do a reopen, I see the same behavior…
My location section in the nginx-configuration:

location / {
    proxy_pass http://localhost:8123;
    proxy_set_header Host $host;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
    proxy_intercept_errors on;

Try the iOS beta app

Use the credentails that you normally use to log in to the home assistant web front end.