This product is either discontinued or we cannot get that from suppliers.
Synology D4ES01-4G, RAM Module, DDR4 SDRAM, FF SoDIMM, ECC, 260-pin.
The 4GB DDR4 SO-DIMM ECC Memory Module from Synology provides 4GB of DDR4 ECC memory. This memory has a 260-pin SO-DIMM form factor and is unbuffered, or not registered.