TypeError when generating continuation token - payload not JSON-serializable

[jmathur427]

• Package Name: azure-core
• Package Version: Installed via virtual environment (1.38.0)
• Operating System: macOS 26.2 (25C56)
• Python Version: 3.13

Describe the bug
A TypeError is raised when the Azure SDK polling framework attempts to generate a continuation token for a long-running operation. The exception indicates that the payload used for token generation is not JSON-serializable, which prevents continuation tokens from being created.
This issue disrupts workflows that rely on resuming, retrying, or persisting long-running operations using continuation tokens.

To Reproduce
Steps to reproduce the behavior:

1. Execute an Azure SDK operation that uses the polling mechanism (long-running operation).
2. Allow the operation to reach a point where a continuation token is requested (e.g., calling poller.continuation_token()).
3. The SDK attempts to serialize the initial response to generate the continuation token.
4. A runtime exception is thrown.

Exception stack trace:

TypeError: Unable to generate a continuation token for this operation. Payload is not JSON-serializable.

File ".../azure/core/polling/_poller.py", line 283, in continuation_token
    return self._polling_method.get_continuation_token()

File ".../azure/core/polling/_poller.py", line 165, in get_continuation_token
    return _encode_continuation_token(self._initial_response)

File ".../azure/core/polling/_utils.py", line 138, in _encode_continuation_token
    raise TypeError(
        "Unable to generate a continuation token for this operation. "
        "Payload is not JSON-serializable."
    )

Expected behavior
The SDK should either:

• Gracefully handle non-JSON-serializable fields when generating continuation tokens, or
• Provide a documented mechanism to customize or override continuation token generation, or
• Clearly document which operations or payload structures are incompatible with continuation tokens.

At a minimum, the error should provide actionable guidance on how to mitigate or work around the issue.

Additional context

• This issue occurs at runtime and is not detectable during development or static analysis.
• The failure prevents safe retry or resume of long-running operations in production environments.
• The error message does not indicate which part of the response payload is non-serializable, making diagnosis difficult.
• Guidance on known limitations, recommended workarounds, or planned fixes would be highly appreciated.
• This issue is coming for begin_delete and begin_create_or_update operations.

[kashifkhan]

@jmathur427 thank you for the feedback. Will you be able to share some code that shows how to reproduce the error or the SDK that you were using this with ?

[github-actions]

Hi @jmathur427. Thank you for opening this issue and giving us the opportunity to assist. To help our team better understand your issue and the details of your scenario please provide a response to the question asked above or the information requested above. This will help us more accurately address your issue.

[jmathur427]

@jmathur427 thank you for the feedback. Will you be able to share some code that shows how to reproduce the error or the SDK that you were using this with ?

@kashifkhan - Certainly, here’s the sample code that fails at the last line.

# env_params contains the information of client for authentication

client_secret = ClientSecretCredential(
    client_id=env_params["azure_client_id"],
    client_secret=env_params["azure_client_secret"],
    tenant_id=env_params["azure_tenant_id"],
)

subscription_id = env_params["subscription_id"]
client =  SqlManagementClient(
    credential=client_secret, subscription_id=subscription_id
)

async_delete = client.managed_databases.begin_delete(
    resource_group_name=resource_group,
    managed_instance_name=managed_instance_name,
    database_name=database_name,
    polling=False,
)

status = Status.PENDING
continuation_token = async_delete.continuation_token()

[kashifkhan]

@jmathur427 thank you for the repro. Why is polling set to False and then a continuation token is requested? The continuation token is used to fetch a result from a polling operation at a later point, so this scenario is unclear

[github-actions]

Hi @jmathur427. Thank you for opening this issue and giving us the opportunity to assist. To help our team better understand your issue and the details of your scenario please provide a response to the question asked above or the information requested above. This will help us more accurately address your issue.