I'm trying to write a Corrective Action to add a datafile to a tablespace

Cloud Control 12.1.0.2.0

I would have thought this would be a pretty common action but I can't find anything online describing how it is done.

I have created the corrective action named ADD_DATAFILE to run as a SQL script

For the Script I entered

WHENEVER SQLERROR EXIT FAILURE;

alter tablespace &1 add datafile '+DG1' size 1000M autoextend on maxsize 32000M;

With the following parameter (no idea if %metric% is actually the tablespace name).

%metric%

I set up named credentials for both the Instance and the Host.  (I've verified both of the named credentials).

I trigger the metric by shrinking a data file to make the pct_free over the threshold.