As part of the StreamGrp component (under Instruments) the NoStreams is not defined as Required. Do we know why this is not marked as required?
For cancels and quotes we have not included NoStreams as a field and there is some concern that we may not be consistent with other component requirements.
NoStreams(40049) is the NumInGrp field to count the number of instances of the repeating group StreamGrp. It cannot be defined as required in general because the entire group is optional. Only if you intend to detail the swap streams associated with the instrument then you have to use the repeating group and NoStreams(40049) as well as StreamType(40050). If you do not need this information on cancels and quotes then you can omit it in these cases and only provide it in other cases.
This is a general principle applicable to all optional repeating groups in FIX.
Thanks @hanno.klein