I have made a custom tool that I want to use in another custom tool. I have loaded the toolbox that it is in using arcpy.ImportToolbox.
I keep getting the following error:

The error occurs at "arcpy.AddPivotField_tsa_tools"...
This tool really does exist. I listed the tools from this toolbox within the script and it correctly listed this tool, including the alias "_tsa_tools" It seems to have access to this tool.
Most obvious explanation is that I am entering it wrong, but I'm not. I've tried many many times.
I have a feeling this is a facepalm. I'm overlooking something obvious. Is there something that needs to be done to "tell" arcpy that this tool exists?
Thank you for any assistance you may be able to provide.