elsa-workflows/elsa-core · error · OutputConversionException

Output converter ' ' failed during for output ' ' of…

Error message

Output converter '{converterId}' failed during {stage} for output '{outputName}' of activity '{activityId}'.

What it means

OutputConverterInvoker.Invoke throws an OutputConversionException with this message template when the configured converter id cannot be resolved from the IOutputConverterRegistry (stage = Resolution). Every converter failure in the pipeline is normalized into this single message; the exception's stage property tells you which step failed.

Solutions

1. Correct the converter id in the output binding configuration to match a registered converter.
2. Register the output converter feature/module (or the converter itself with the registry) at host startup.
3. List registered converters at startup (inspect IOutputConverterRegistry) and verify the configured id exists.
4. Catch OutputConversionException and inspect its Stage/ConverterId properties to pinpoint which converter configuration is wrong.

Example fix

// before
output.Converter = new OutputConverterConfiguration { Id = "json-converter" };
// after
output.Converter = new OutputConverterConfiguration { Id = "my-registered-converter-id" }; // id present in IOutputConverterRegistry

var registry = serviceProvider.GetRequiredService<IOutputConverterRegistry>();
if (output.Converter != null && registry.Find(output.Converter.Id) == null)
    throw new InvalidOperationException($"Converter '{output.Converter.Id}' is not registered.");

bool IsConverterRegistered(IOutputConverterRegistry registry, string? id) => id != null && registry.Find(id) != null;

try { var value = invoker.Invoke(ctx, output, outputName, sourceType, raw, destination); }
catch (OutputConversionException e) when (e.Stage == OutputConversionFailureStage.Resolution)
{ logger.LogError(e, "Converter {Id} not found for output {Output}", output.Converter?.Id, outputName); }

When it happens

Trigger: An output binding's Converter configuration references a converter id (configuration.Id) that is not registered in IOutputConverterRegistry when Invoke runs, so registry.Find returns null.

Common situations: Typo in the converter id in the activity/output binding configuration; the converter feature/module registering the converter was not added to the host; converter registered under a different key or DI key mismatch.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

• Output converter ' ' cannot use open-generic source or…
• Output converter ID ' ' is registered more than once or…
• Output converter IDs cannot be empty.
• Output converter registration
• Secret ' ' was not found.

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/e35c30d17d9053e1. Report an issue: GitHub.

Appendix: source

Thrown at src/modules/Elsa.Workflows.Core/Services/OutputConverterInvoker.cs:25

/// <inheritdoc />
public class OutputConverterInvoker(
    IOutputConverterRegistry registry,
    IOutputConverterSettingsValidator settingsValidator) : IOutputConverterInvoker
{
    /// <inheritdoc />
    public object? Invoke(
        ActivityExecutionContext activityExecutionContext,
        Output output,
        string outputName,
        Type sourceType,
        object value,
        OutputBindingDestination destination)
    {
        var configuration = output.Converter ?? throw new InvalidOperationException("The output binding has no converter configuration.");
        var descriptor = registry.Find(configuration.Id);

        if (descriptor == null)
            throw CreateException(OutputConversionFailureStage.Resolution);

        if (!IsRuntimeValueCompatible(value, sourceType) || !descriptor.SourceType.IsAssignableFrom(sourceType))
            throw CreateException(OutputConversionFailureStage.SourceCompatibility);

        if (!OutputConverterRegistry.IsAssignableToDestination(descriptor.ResultType, destination.Type))
            throw CreateException(OutputConversionFailureStage.ResultValidation);

        IOutputConverter converter;

        try
        {
            converter = activityExecutionContext.WorkflowExecutionContext.ServiceProvider
                .GetRequiredKeyedService<IOutputConverter>(configuration.Id);
        }
        catch (Exception e)
        {
            throw CreateException(OutputConversionFailureStage.Resolution, e);
        }

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