Available On field display nothing after import Witholding Tax Code

I try to import Witholding Tax Code using csv file, on the Available On field i put "Purchases" Value same as the value when manually create the Witholding Tax Code. But after import process are finish and the result are successfully, when i check on the the WHT Code are generated but the Available On field don't have any value and i cannot delete or update the data.

How can i fix this ? anyone can help me?

Regards,

Hendra