A Send task has an outgoing message flow; error message says it needs a sequence flow

[chrisesposito4]

I have 2 send tasks; 1 of them is in a pool; the other is not. Both have outgoing message flows but no outgoing sequence flows.
Both also have little encircled red 'x's with the message 'ERROR: A Task must have least one outgoing sequence flow'. In both cases the message flow is going to an IntermediateCatchEvent and crosses the boundary between pool and no-pool.

 A puzzle here is that I have other instances of send tasks with outgoing message flows (but not sequence flows) that go to events that go to other send tasks (so the local context is the same) , all without error.

I didn't think that send tasks needed an outgoing sequence flow. I can send along the problem model if that helps.

[rsoika]

Hi @chrisesposito4 , thanks for your question and for your interest in Open-BPMN! 🙂
You've actually discovered the correct behavior according to the BPMN 2.0 specification. I think the error message you're seeing is valid.

According to the BPMN 2.0 spec, all flow objects — including Send Tasks — must have at least one outgoing Sequence Flow, provided your process contains Start or End Events. The key distinction is:

• Sequence Flow controls the process flow within a pool
• Message Flow represents communication between pools/participants

A Message Flow does not replace the need for a Sequence Flow. They serve different purposes. Think of it this way: the Sequence Flow tells the process engine "what to do next," while the Message Flow tells it "who to communicate with."

Simply add an End Event after your Send Task and connect them with a Sequence Flow.

So your model should look something like:
[Send Task] --sequence flow--> [End Event]
...with the Message Flow going from the Send Task (or a Message End Event) across to the IntermediateCatchEvent in the other pool.

Feel free to share your model if you'd like us to take a closer look!

[chrisesposito4]

Thanks for the clarification Ralph. I have attached the model in question so you can see an example. The model is about a purchase and sale of an item (in this case a backpack). The top section is what the buyer (denoted 'B') does, and the bottom pool is what the seller (denoted 'S') does. Price and terms are negotiated and may be accepted or rejected. Numeric suffixes (e.g., B4) are a step that an entity does (in this case, the buyer).

As you can see from the diagram, the Send Task marked with S2 has both 2 outgoing flows (1 message,1 sequence) and so does not have any error indicator. Send tasks B5 and S7 have only a message flow and are the 2 marked with an error. Your explanation makes sense.
Better event-gate model.vs.zip

[rsoika]

I took a look into your model. In this concrete case I would recommend to use an Intermediate Throw Event. So the situation should loook like this:

[chrisesposito4]

Thanks for the fix, Ralph.

…

________________________________ From: Ralph Soika ***@***.***> Sent: Monday, January 26, 2026 12:02 AM To: imixs/open-bpmn ***@***.***> Cc: Chris Esposiro ***@***.***>; Mention ***@***.***> Subject: Re: [imixs/open-bpmn] A Send task has an outgoing message flow; error message says it needs a sequence flow (Discussion #437) I took a look into your model. In this concrete case I would recommend to use an Intermediate Throw Event. So the situation should loook like this: grafik.png (view on web)<https://github.com/user-attachments/assets/49df37ee-4674-40bd-a46f-5007d7dba06e> — Reply to this email directly, view it on GitHub<#437 (reply in thread)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/BJZB6PKHVXJYVGGTOOEEZX34IXC2TAVCNFSM6AAAAACSZBMFTGVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTKNRQGMZTIMQ>. You are receiving this because you were mentioned.Message ID: ***@***.***>