E: Package 'ngcp-keyring' has no installation candidate

[Kuanlin-Chen]

Followed the installing guidance to install ngcp-keyring and ngcp-rtpengine on my debian bookworm docker but got the error message listed below.

Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Package ngcp-keyring is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'ngcp-keyring' has no installation candidate

Is there anything I can do to solve this issue? I would appreciate any idea or help.