How to build Gnucash in /home/<user>/opt?

[egrath]

This issue has been discussed over here:

No network in toolbox container

I successfully created my first container as suggested in [solved] Running windows applications on eos flatpak error install but I cannot install anything inside the container. Apparently I don’t have network connectivity inside. Both dnf & yum complain “failed to synchronize cache for repo ‘fedora-modular’”. Running dnf -v hinted at a network problem. In the container a ping mirrors.fedoraproject.org fails, but outside it works. Any help and or ideas are welcome … eos-diagnostic-191004_12255…