Cannot create NPC repeating attribute with setattr

I'm trying to create multi-creature sheets, like for the Bag of Tricks.  I need to modify the number of traits on the sheet depending on the selection.  The command delattr works great, but when I use setattr when no attribute exists, I get an error.  Works to overwrite one, but it won't create one.  An example of my script is !setattr --silent --charid @{Tan Bag of Tricks|character_id} --repeating_npctrait_$2_name|Pack Tactics --repeating_npctrait_$2_description|'The jackal has advantage on an attack roll against a creature if at least one of the jackal's allies is within 5 ft. of the creature and the ally isn't incapacitated.'

There's an example on the wiki of adding to a repeating section - you'll need to get rid of the index ($2), as not even the mod script is allowed to dictate the index of a new repeating row - it's automatically indexed at the end of the repeating section. Replace it with the keyword -CREATE

Like this? !setattr --silent --charid @{Tan Bag of Tricks|character_id} --repeating_npctrait_CREATE_name|Pack Tactics --repeating_npctrait_CREATE_description|'The jackal has advantage on an attack roll against a creature if at least one of the jackal's allies is within 5 ft. of the creature and the ally isn't incapacitated.'

I tried !setattr --silent --charid @{Tan Bag of Tricks|character_id} --repeating_npctrait_CREATE_name|Pack Tactics !setattr --silent --charid @{Tan Bag of Tricks|character_id} --repeating_npctrait-CREATE_name|Pack Tactics !setattr --silent --charid @{Tan Bag of Tricks|character_id} --repeating_npctrait-CREATE !setattr --CREATE --silent --charid @{Tan Bag of Tricks|character_id} --repeating_npctrait !setattr --create --silent --charid @{Tan Bag of Tricks|character_id} --repeating_npctrait none of which worked.  What's the correct syntax?

You were super close - the $# in the repeating section need to be replaced by -CREATE, so there's an underscore and  dash in the repeating section: !setattr --silent --charid @{Tan Bag of Tricks|character_id} --repeating_npctrait _- CREATE_name|Pack Tactics So the full thing will be: !setattr --silent --charid @{Tan Bag of Tricks|character_id} --repeating_npctrait_-CREATE_name|Pack Tactics --repeating_npctrait_-CREATE_description|'The jackal has advantage on an attack roll against a creature if at least one of the jackal's allies is within 5 ft. of the creature and the ally isn't incapacitated.'

Very nice.  Worked like a charm.  Thank you very much!