Ok so I've switched to a Field Auto Action.
The action is manually triggered using the below URL.
index.php?option=com_comprofiler&view=pluginclass&plugin=cbautoactions&action=action&actions=97&Itemid=181&fav=350
Plan was to pick up that "fav" query string value and set the field. So following your advice (simple first, input validated after) I've set...
Field: cb_profile_title
Operator: Set
Value: [get_fav]
However when I trigger the action the cb_profile_title becomes "[get_fav]" rather than "350".
I'm also echoing out under the out tab and [get_fav] is showing 350 on the output. I must be missing something??
Substitutions is on.