It looks like the issue is as you suggested, that I need to supply the TPLNR as the function location to BAPI_ALM_NOTIF_CREATE.
Is there an existing BAPI that I can call from an external application to convert the Functional Location string to it's corresponding TPLNR?
I noticed that you can look up the TPLNR number in the IFLOS table. Is there any way to interrogate the IFLOS table using BAPI calls from an external application?