The FIX protocol specifies that the checjsum should be 3 ASCII characters. I am observing that simplefix (1.0.16) sometimes sends less, i.e., 2 characters:
2023-09-11 13:16:44,485 : process_buffer : INFO : Sending FIX heartbeat message 8=FIX.4.4|9=67|35=0|49=QAORG1_UAT|56=STP_ROUTER_UAT|34=2|52=20230911-17:16:44.485|10=88
The FIX protocol specifies that the checjsum should be 3 ASCII characters. I am observing that simplefix (1.0.16) sometimes sends less, i.e., 2 characters: 2023-09-11 13:16:44,485 : process_buffer : INFO : Sending FIX heartbeat message 8=FIX.4.4|9=67|35=0|49=QAORG1_UAT|56=STP_ROUTER_UAT|34=2|52=20230911-17:16:44.485|10=88