Cannot query non 'TR.XXX' fields using /data/datagrid/beta1/ API

I am trying to use the /data/datagrid/beta1/ API, but notice that any fields queried that do not start with TR such as CURRENCY, RDN_EXCHID, RDN_EXCHD2 or LOT_SIZE are not recognized as valid fields and thus do not even generate a response. Does anyone know if there is a limitation to this api to only accept TR.XXX fields such as TR.Sedol for example? I already understood that CF_XXX fields are not accepted as they are Eikon mapppings. Eikon provided me with the real data feed mapping for these various fields but they do not start with 'TR', so they are not being accepted by this api.