As mentioned, all FIX service monitors will output diagnostic information to the service logs. This information can be useful in diagnosing application related problems such as missing or incorrectly specified parameters.

For example, upon receiving a new market data subscription request the subscription manager will output information regarding its current reference counts for that symbol and what (if anything) it intends to send to the market.

However, sometimes it is necessary to dig deeper and establish exactly what is being sent to and received from the target system. In these cases it is best to refer to the FIX message log (as discussed above) to diagnose the problem.