If performing a write, use data/transforms/lookups
If performing a read and you need fields_list, use data/transforms/lookups
For everything else, use configs/conf-transforms
Generally, it is recommended that you avoid using data/transforms/lookups/ since this endpoint triggers some activity that can cause some unnecessary performance reduction and will generate a substantial number of log messages in the internal index.
If you need to access ACL information (i.e. namespace and owner) then you will need to use configs/conf-transforms since properties/transforms/ won't include it.