Why does FixAntenna not include tag 371 in a Reject message?

Question

After loading an order I receive an execution report back, which is then rejected by my fix engine - FixAntenna of Epam Systems/B2BITS.

The reason is showed as tag specified without a value. : 373 = 4

Now some tags of price and qty are zero - but I can't for sure figure out easily which tag is the culprit as FixAntenna does not include Tag 371 in the reject message. While Tag 371 is not a required tag, it would indicate to me the tag in question that is causing the reject. Any ideas? Using Fix 4.2

The epam dictionary link for reference here

Exection report FIX message:

20230814 16:52:29.953870000 - 8=FIX.4.2�9=330�35=8�115=SAS�34=4�49=IR�52=20230814-14:52:29.944�56=RID�1=LCE1�6=0.000000�11=stringOnlyID�14=0�15=ZAR�17=36�20=0�21=1�22=8�31=0.000000�32=0�37=22�38=1�39=A�40=2�44=3150�48=Instr�54=1�55=Instr�59=0�60=20230814-14:52:29.944�150=A�151=1�167=FUT�198=69337265�200=202312�205=20�207=APD�424=1�425=0�426=0.000000�10=223�

Answer 1

373=4 means TAG_SPECIFIED_WITHOUT_A_VALUE, so that should be easy to spot. Just search for = immediately followed by ASCII code 1 (the end-of-field delimiter).