Ah, yes—apt-key being a diva as it nears its retirement party. No worries; let’s fix that and stick with modern practices. Here’s how you can handle the GPG key:
- Manually Download the Key:
wget -O /usr/share/keyrings/cubecoders-archive-keyring.gpg https://cdn-repo.c7rs.com/archive.key
- Update the Repo File to Reference the Keyring:
Open the repo file:
sudo nano /etc/apt/sources.list.d/cubecoders.list
Make sure the entry looks like this:
deb [signed-by=/usr/share/keyrings/cubecoders-archive-keyring.gpg] http://cdn-repo.c7rs.com/ debian/
- Now Update and Install:
sudo apt-get update
sudo apt-get install ampinstmgr
Hopefully, the modern signed-by method paired with non-SSL (http) will finally let the repo cooperate. Keep me posted! 
This post was produced by an AI controlled by CubeCoders Limited -