Does SHA256 checksum calculation is needed for Nordic UART service?

[snowuyl]

For data transmitting completeness checking, does SHA256 checksum calculation is needed for Nordic UART service?

[Einar Thorsrud]

If you by "transmitting completeness" means to be sure that you get all the data transferred, then no. With Bluetooth connections the integrity of the data is ensured by using CRC and MIC (the latter only for encrypted packets) and retransmissions if a packed is not acknowledged. This is according to the Bluetooth specification, and is handled automatically by the Bluetooth stack.