Sample fails if PAYLOAD_SIZE_BYTES exceeds 10MB

[kabcampbell]

Which sample is affected?

Large Payload Support — .NET Isolated Durable Functions

Describe the bug

Is there a hard limit of 10MB for large payloads? If I set the PAYLOAD_SIZE_BYTES to a value over 10MB the sample throws the following error:

[2026-07-08T18:09:03.524Z] Function 'StartLargePayload', Invocation id 'daea11ca-be8f-47ef-8b5a-000be29a8c8d': An exception was thrown by the invocation.
[2026-07-08T18:09:03.525Z] Result: Function 'StartLargePayload', Invocation id 'daea11ca-be8f-47ef-8b5a-000be29a8c8d': An exception was thrown by the invocation.
Type:
Exception: Grpc.Core.RpcException: Status(StatusCode="Internal", Detail="Failed to start instance with ID a73c55d84bb54fdd8555518ae3adb983.
Inner Exception message: Payload size 10742 KB exceeds the configured maximum of 10240 KB. Reduce the payload size or increase the max payload size limit..")
[2026-07-08T18:09:03.527Z] at Grpc.Net.Client.Internal.Retry.RetryCallBase2.GetResponseCoreAsync() [2026-07-08T18:09:03.528Z] at Microsoft.DurableTask.Client.Grpc.GrpcDurableTaskClient.ScheduleNewOrchestrationInstanceAsync(TaskName orchestratorName, Object input, StartOrchestrationOptions options, CancellationToken cancellation) [2026-07-08T18:09:03.529Z] at LargePayload.LargePayloadOrchestration.HttpStart(HttpRequestData req, DurableTaskClient client, FunctionContext executionContext) in C:\VSProjects\Samples\LargePayload\LargePayloadOrchestration.cs:line 26 [2026-07-08T18:09:03.531Z] at LargePayload.DirectFunctionExecutor.ExecuteAsync(FunctionContext context) in C:\VSProjects\Samples\LargePayload\obj\Debug\net8.0\Microsoft.Azure.Functions.Worker.Sdk.Generators\Microsoft.Azure.Functions.Worker.Sdk.Generators.FunctionExecutorGenerator\GeneratedFunctionExecutor.g.cs:line 32 [2026-07-08T18:09:03.532Z] at Microsoft.Azure.Functions.Worker.OutputBindings.OutputBindingsMiddleware.Invoke(FunctionContext context, FunctionExecutionDelegate next) in /_/src/DotNetWorker.Core/OutputBindings/OutputBindingsMiddleware.cs:line 13 [2026-07-08T18:09:03.533Z] at Microsoft.Azure.Functions.Worker.Extensions.Http.AspNetCore.FunctionsHttpProxyingMiddleware.Invoke(FunctionContext context, FunctionExecutionDelegate next) in /_/extensions/Worker.Extensions.Http.AspNetCore/src/FunctionsMiddleware/FunctionsHttpProxyingMiddleware.cs:line 54 [2026-07-08T18:09:03.534Z] at Microsoft.Azure.Functions.Worker.Extensions.DurableTask.DurableTaskFunctionsMiddleware.Invoke(FunctionContext functionContext, FunctionExecutionDelegate next) in /_/src/Worker.Extensions.DurableTask/DurableTaskFunctionsMiddleware.cs:line 31 [2026-07-08T18:09:03.535Z] at Microsoft.Azure.Functions.Worker.FunctionsApplication.InvokeFunctionAsync(FunctionContext context) in /_/src/DotNetWorker.Core/FunctionsApplication.cs:line 83 Stack: at Grpc.Net.Client.Internal.Retry.RetryCallBase2.GetResponseCoreAsync()
[2026-07-08T18:09:03.536Z] at Microsoft.DurableTask.Client.Grpc.GrpcDurableTaskClient.ScheduleNewOrchestrationInstanceAsync(TaskName orchestratorName, Object input, StartOrchestrationOptions options, CancellationToken cancellation)
[2026-07-08T18:09:03.537Z] at LargePayload.LargePayloadOrchestration.HttpStart(HttpRequestData req, DurableTaskClient client, FunctionContext executionContext) in C:\VSProjects\Samples\LargePayload\LargePayloadOrchestration.cs:line 26
[2026-07-08T18:09:03.538Z] at LargePayload.DirectFunctionExecutor.ExecuteAsync(FunctionContext context) in C:\VSProjects\Samples\LargePayload\obj\Debug\net8.0\Microsoft.Azure.Functions.Worker.Sdk.Generators\Microsoft.Azure.Functions.Worker.Sdk.Generators.FunctionExecutorGenerator\GeneratedFunctionExecutor.g.cs:line 32
[2026-07-08T18:09:03.539Z] at Microsoft.Azure.Functions.Worker.OutputBindings.OutputBindingsMiddleware.Invoke(FunctionContext context, FunctionExecutionDelegate next) in //src/DotNetWorker.Core/OutputBindings/OutputBindingsMiddleware.cs:line 13
[2026-07-08T18:09:03.541Z] at Microsoft.Azure.Functions.Worker.Extensions.Http.AspNetCore.FunctionsHttpProxyingMiddleware.Invoke(FunctionContext context, FunctionExecutionDelegate next) in //extensions/Worker.Extensions.Http.AspNetCore/src/FunctionsMiddleware/FunctionsHttpProxyingMiddleware.cs:line 54
[2026-07-08T18:09:03.542Z] at Microsoft.Azure.Functions.Worker.Extensions.DurableTask.DurableTaskFunctionsMiddleware.Invoke(FunctionContext functionContext, FunctionExecutionDelegate next) in //src/Worker.Extensions.DurableTask/DurableTaskFunctionsMiddleware.cs:line 31
[2026-07-08T18:09:03.543Z] at Microsoft.Azure.Functions.Worker.FunctionsApplication.InvokeFunctionAsync(FunctionContext context) in //src/DotNetWorker.Core/FunctionsApplication.cs:line 83.
[2026-07-08T18:09:03.596Z] Executed 'Functions.StartLargePayload' (Failed, Id=daea11ca-be8f-47ef-8b5a-000be29a8c8d, Duration=1536ms)
[2026-07-08T18:09:03.597Z] System.Private.CoreLib: Exception while executing function: Functions.StartLargePayload. System.Private.CoreLib: Result: Failure
Type: Grpc.Core.RpcException
Exception: Status(StatusCode="Internal", Detail="Failed to start instance with ID a73c55d84bb54fdd8555518ae3adb983.
Inner Exception message: Payload size 10742 KB exceeds the configured maximum of 10240 KB. Reduce the payload size or increase the max payload size limit..")
Stack: at Grpc.Net.Client.Internal.Retry.RetryCallBase`2.GetResponseCoreAsync()
[2026-07-08T18:09:03.599Z] at Microsoft.DurableTask.Client.Grpc.GrpcDurableTaskClient.ScheduleNewOrchestrationInstanceAsync(TaskName orchestratorName, Object input, StartOrchestrationOptions options, CancellationToken cancellation)
[2026-07-08T18:09:03.600Z] at LargePayload.LargePayloadOrchestration.HttpStart(HttpRequestData req, DurableTaskClient client, FunctionContext executionContext) in C:\VSProjects\Samples\LargePayload\LargePayloadOrchestration.cs:line 26
[2026-07-08T18:09:03.602Z] at LargePayload.DirectFunctionExecutor.ExecuteAsync(FunctionContext context) in C:\VSProjects\Samples\LargePayload\obj\Debug\net8.0\Microsoft.Azure.Functions.Worker.Sdk.Generators\Microsoft.Azure.Functions.Worker.Sdk.Generators.FunctionExecutorGenerator\GeneratedFunctionExecutor.g.cs:line 32
[2026-07-08T18:09:03.604Z] at Microsoft.Azure.Functions.Worker.OutputBindings.OutputBindingsMiddleware.Invoke(FunctionContext context, FunctionExecutionDelegate next) in //src/DotNetWorker.Core/OutputBindings/OutputBindingsMiddleware.cs:line 13
[2026-07-08T18:09:03.606Z] at Microsoft.Azure.Functions.Worker.Extensions.Http.AspNetCore.FunctionsHttpProxyingMiddleware.Invoke(FunctionContext context, FunctionExecutionDelegate next) in //extensions/Worker.Extensions.Http.AspNetCore/src/FunctionsMiddleware/FunctionsHttpProxyingMiddleware.cs:line 54
[2026-07-08T18:09:03.608Z] at Microsoft.Azure.Functions.Worker.Extensions.DurableTask.DurableTaskFunctionsMiddleware.Invoke(FunctionContext functionContext, FunctionExecutionDelegate next) in //src/Worker.Extensions.DurableTask/DurableTaskFunctionsMiddleware.cs:line 31
[2026-07-08T18:09:03.609Z] at Microsoft.Azure.Functions.Worker.FunctionsApplication.InvokeFunctionAsync(FunctionContext context) in //src/DotNetWorker.Core/FunctionsApplication.cs:line 83
[2026-07-08T18:09:03.611Z] at Microsoft.Azure.Functions.Worker.Handlers.InvocationHandler.InvokeAsync(InvocationRequest request) in /_/src/DotNetWorker.Grpc/Handlers/InvocationHandler.cs:line 91.

Steps to reproduce

1. In local.settings.json, set "PAYLOAD_SIZE_BYTES": "11000000"
2. Run the sample

Expected behavior

Large payload offload works fine for values under the 10MB threshold described in the error. Since no hard limit of 10MB is described anywhere in the DTS large payload support documentation, I would expect that it would continue to offload payloads of any size.

Environment