Export Multiple Animations to a Single FBX

Based on the documentation, it sounds like it should be possible to export multiple animations (takes) into a single FBX file. I can't get it to work. Here's what my script looks like:

for group in getAnimationNames():
for anim in group[1]:
inputFile = "C:/Users/A1849763/Nextcloud/NIU/Papers/Working/Internal Auditing Experiment/Avatar/FaceFX/Interviewer_FaceFX_Import.fbx"
outputFile = "C:/Users/A1849763/Nextcloud/NIU/Papers/Working/Internal Auditing Experiment/Avatar/FaceFX/Interviewer.fbx"
issueCommand('fbx -keyprecision 0.001 -of "%s" -if "%s" -group "%s" -anim "%s" -tn "%s";'%(outputFile, inputFile, group[0], anim, anim))

What am I missing? Don't I need to write to the same out FBX? But this overwrites the existing animations, so I'm only left with one animation in the FBX.