If you have selected on the page top a "Org Example" and a "Loc Munich" and in the HostRegistartion Formular you select the "Org Example" and the "Loc - not specified" and then you select a Smart Proxy in the list which is NOT part of the "Loc Munich", then it will still show an error that the Host Registartion Command can not be generated.

a) The tell the customer to have a look at the logs doesn't help and should never happen because some customer users don't have access to the log
b) The Smart Proxy issue should not happen. It should only list Smart Proxies which are usable with the Organization/Location combination.

See https://github.com/theforeman/foreman/pull/10240#issuecomment-2245363949 for more details of the issue.