What field would you use if new orders can be sent with an algorithm name? For instance, the exDest is going to be the venue/broker, but orders will also have a “code” which is used upstream to designate how the order should be handled/routed.
I’ve looked through the spec, and there doesn’t appear to be anything other than field 100, exDest.
FIX has a large number of explicit fields for this purpose, i.e. it depends on what you want to communicate. If it is only about conveying some proprietary “code” that is interpreted upstream then you can use the OrderAttributeGrp with OrderAttributeType(2594) having a user-defined value of 1000 or higher with OrderAttributeValue(2595) containing the actual identifier.
If you are subject to a regulatory environment requiring you to register algorithms with the NCA you may use ComplianceID(376) for the identifier and optionally ComplianceText(2404) for a short description of the algo.