In Boomi, we often design the integration process to run in a serial mode by having a Parent process that invokes Sub process.
This is really helpful if we have a business flow which we need to make sure that the parent record (e.g, Customer) is synced into the target system before the related record (e.g, Sales Order) is being synced. However, this design is not that handy when it comes to retrying error document. As you all know that Boomi allows you to retry an error document in the Process Monitoring console. This only works for the document that is related to the Boomi process that is attached to an environment directly and deployed.
As a workaround, you will need to attach and deploy the related Sub process to an environment and just let it sit there without having any scheduler.