Standy Database clinprt fail to add temp files

After we have cloned prod to ROPROD using the cerner scripts, the database(ROPROD) will not let us add Temp files to the temp tablespace.

Error Code/Message: Database error: ORA-01157: cannot identify/lock data file 4097 - see DBWR trace file ORA-01110: data

Connected as sysdba in read-only mode

SQL>

ALTER TABLESPACE TEMP ADD TEMPFILE '+DG_CISRPT_REDO_01' SIZE 500M AUTOEXTEND ON NEXT 250M MAXSIZE 30720M;

ORA-00604: error occurred at recursive SQL level 1

ORA-16000: database open for read-only access

ORA-06512: at line 1066

ORA-16000: database open for read-only access