12.1.3 does not support excel templates.
You need to apply the patch mentioed below in the document. This will enable the XLS type in aplication lookup XDO_FILE_TYPE
R12: How to add Microsoft Excel as Type to the Create Template List of Values in BI Publisher (Doc ID 1343225.1)
"After Patch 12415414 is applied do the following to enable EXCEL output option for BI publisher templates:"
That patch is only for a specific FSG issue, it states:
Applying these patches do NOT endorse Excel templates in EBS BI Publisher.
The patches here are specifically for an FSG template issue even though these are XDO patches.
We applied this patch for same issue and it worked for us.
Useful to know, Thanks Brajesh.