Trying to convert data into JSON for external post API call


I’m having difficulty getting results from my database into JSON data for a external POST call to a 3rd party service. I have experimented with several of the JSON converter plugins (JSONator, jsoNata, etc.) but for some reason it appears they are stripping several fields when they have 0 values. Any suggestions on a workaround for this? it is necessary to pass the '0’s.