Can't log in to dashboard

Setup of Traefik 1.7 is up and running. Reverse proxy with 3 Docker (SWARM) apps is working regularly, but I can't log in to the dashboard. The username / PW is not accepted.

PW is generated with
echo $(htpasswd -nb user password) | sed -e s/\$/\$\$/g
and copied into basic_auth.

My traefik.toml:
defaultEntryPoints = ["http", "https"]

logLevel = "INFO"

[entryPoints]
[entryPoints.http]
address = ":80"
[entryPoints.http.redirect]
entryPoint = "https"
[entryPoints.https]
address = ":443"
[entryPoints.https.tls]

[acme]
storage = "acme.json"
entryPoint = "https"
onDemand = false
onHostRule = true
[acme.httpChallenge]
entryPoint = "http"

[api]

[ping]
entryPoint = "https"

[docker]
endpoint = "unix:///var/run/docker.sock"
watch = true
exposedByDefault = false

When I try to reach the dashboard via https://traefik.domain.de/dashboard/ I get the request to enter username and password and: nothing.

Where is the fault? Anybody got an idea where to look?

Thank you.

Marc