Transfers N-acetylgalactosamine (GalNAc) from UDP-GalNAc to N-acetylglucosamine-beta-benzyl with a beta-1,4-linkage to form N,N'-diacetyllactosediamine, GalNAc-beta-1,4-GlcNAc structures in N-linked glycans and probably O-linked glycans. an N-acetyl-beta-D-glucosaminyl derivative + UDP-N-acetyl-alpha-D-galactosamine = an N-acetyl-beta-D-galactosaminyl-(1->4)-N-acetyl-beta-D-glucosaminyl derivative + H(+) + UDP Belongs to the chondroitin N-acetylgalactosaminyltransferase family. Beta1,4-N-acetylgalactosaminyltransferase IV