There’s no publicly posted full PDF datasheet or pinout for the exact T4B-6620VDB-1.3 / T4B_Module_V1_2_20170612 board that I could find. KeyStone’s product pages describe the T4B family and a few sellers list practical interface details (see refs), but the full electrical pinout, command-set and board schematic appear to be distributed only to customers / OEM partners.