elsa-workflows/elsa-core · error · BpmnBindingException

The ' ' binding declares the input ' ' more than once. Each…

Error message

The '{activityType}' binding declares the input '{name}' more than once. Each <{NamespacePrefix}:{InputElementName}> must name a distinct input.

What it means

During BPMN import, an activity binding's <elsa:input> child elements must each name a distinct activity input. This error is thrown when two <input> elements in the same binding use the same name, which would make the resulting activity JSON ambiguous.

Solutions

  1. Open the .bpmn file, find the <elsa:binding> for the named activityType, and remove or rename the duplicated <elsa:input name="..."> element so each input is declared once.
  2. If both inputs are intentional, rename the XML input to match the actual distinct activity input names declared on the activity type.
  3. Validate the document again after the edit; the error names the exact activity type and input.

Example fix

// before
<elsa:binding activityType="SendEmail">
  <elsa:input name="Subject">"Hi"</elsa:input>
  <elsa:input name="Subject">"Hello"</elsa:input>
</elsa:binding>
// after
<elsa:binding activityType="SendEmail">
  <elsa:input name="Subject">"Hi"</elsa:input>
</elsa:binding>
Defensive patterns

Strategy: validation

Validate before calling

var inputs = bindingElement.Descendants().Where(e => e.Name.LocalName == "input");
var dupes = inputs.GroupBy(e => (string)e.Attribute("name")).Where(g => g.Count() > 1 && g.Key != null).ToList();
if (dupes.Any()) throw new InvalidOperationException("Duplicate input names: " + string.Join(", ", dupes.Select(d => d.Key)));

Try / catch

try { await importer.ImportAsync(bpmn); }
catch (BpmnBindingException ex) when (ex.Message.Contains("more than once"))
{
    logger.LogError(ex, "Binding XML declares a duplicate input; fix the <elsa:input> elements.");
}

Prevention

When it happens

Trigger: Calling Read (BpmnActivityBindingFormat.Read) on a binding extension element whose <input> children contain a duplicate name attribute value, detected when seenInputNameSet.Add(name) returns false.

Common situations: Hand-editing or copy-pasting binding XML in a .bpmn file; merging two authors' binding declarations; a modeling tool export that duplicates an input element.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/f3d88c7c27619ce5. Report an issue: GitHub.

Appendix: source

Thrown at src/modules/Elsa.Bpmn.Interchange/Binding/BpmnActivityBindingFormat.cs:210

        var activityJson = new JsonObject
        {
            ["type"] = activityType
        };

        // Every name seen so far, in the order the document declares them, so a second <elsa:input> with the same
        // name is refused rather than silently overwriting activityJson[name] and leaving the earlier one's
        // configuration invisible.
        var seenInputNames = new List<string>();
        var seenInputNameSet = new HashSet<string>(StringComparer.Ordinal);

        foreach (var input in element.Children.Where(child => child.Name == InputQName))
        {
            var name = AttributeOf(input, InputNameAttributeName)
                       ?? throw new BpmnBindingException($"An <{NamespacePrefix}:{InputElementName}> element of the '{activityType}' binding declares no '{InputNameAttributeName}'.");

            if (!seenInputNameSet.Add(name))
                throw new BpmnBindingException($"The '{activityType}' binding declares the input '{name}' more than once. Each <{NamespacePrefix}:{InputElementName}> must name a distinct input.");

            seenInputNames.Add(name);
            activityJson[name] = Parse(input.Value, name, activityType);
        }

        IActivity activity;

        try
        {
            activity = activitySerializer.Deserialize(activityJson.ToJsonString());
        }
        catch (Exception exception) when (exception is JsonException or NotSupportedException)
        {
            throw new BpmnBindingException($"The binding to activity type '{activityType}' could not be deserialized: {exception.Message}");
        }

        // Elsa's activity serializer answers an unregistered type with a NotFoundActivity rather than throwing, and
        // that placeholder only fails once it executes — by which time the workflow has already started and the

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