Sync oracle DBs using archive log when not connected to each other
First you need to make sure that the copied database is a standby database. That is not the case in your case. Use duplicate to do that is the easiest way.

Is it possble at all using a not connected database .... yes, but why? To me it looks like a waste of money if there is no decent connectivity.

Restore/open failed because your copy database feels it has the PRIMARY role.
(select database_role from v$database; to check)

There hardly is a simpler way to do this than using rman duplicate. This can be done using a backup, no problem at all. Maybe hiring a real dba can save you lot's of time, money and in the end a disaster.