6-O-sulfation enzyme which catalyzes the transfer of sulfate from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to position 6 of the N-sulfoglucosamine residue (GlcNS) of heparan sulfate. This is the function of HS6ST3 (heparan sulfate 6-O-sulfotransferase 3, Ensembl gene identifier ENSG00000185352).