Issue with Set Participant Data action in Genesys Cloud Architect

Does anyone know how to correctly pass custom variables through an IVR flow using the Set Participant Data action? I am building a flow where I need to update participant attributes dynamically based on previous IVR inputs.

I have tried using the standard JSON payload structure as per the Genesys Docs, but the variables do not seem to persist to the next step.

Here is the JSON payload I am using:

{
 "data": {
 "custom_var_1": "{{inputs.input_1}}",
 "custom_var_2": "{{inputs.input_2}}"
 }
}

When I check the flow logs, the action completes with a 200 OK status, but subsequent actions that reference {{participant.data.custom_var_1}} return null values. I have verified that inputs.input_1 contains the expected value from the previous step.

Is there a specific format required for the data object? Or do I need to use a different method to ensure the data is available in the same flow execution? Any code examples or working configurations would be appreciated.