Problem installing chart with cli

I understand installing a custom chart works as:
rancher app install ./my/chart/ my-chart
But I only get the following error message:

FATA[0000] Bad response statusCode [404]. Status [404 Not Found]. Body: [baseType=error, code=NotFound, message=failed to find resource by id] from []

How can I get more information about the failure? Maybe in any log? (--debug does not help)

I fixed some variables after checking with helm lint and helm install --dry-run. (By the way, I miss this options in rancher cli.)

After running helm pack ./my/chart I get another error message when running app install ./chart-0.1.0.tgz/ my-chart:

FATA[0000] Bad response statusCode [422]. Status [422 Unprocessable Entity]. Body: [baseType=error, code=InvalidFormat, fieldName=name, message=InvalidFormat 422: invalid value -5msh3: a DNS-1123 label must consist of lower case alphanumeric characters or '-', and must start and end with an alphanumeric character (e.g. 'my-name',  or '123-abc', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?')] from []

No Idea which field name it is about. The chart works with helm install ....

rancher --version: rancher version v2.3.2 and also after update to cli v2.4.0 (with server v2.4.2)