I am trying to setup a Inbound New Guest appointment flow with person accounts but unable to do it . Its showing this error:

This error occurred when the flow tried to create records: REQUIRED_FIELD_MISSING: Required fields are missing: [LastName]. You can look up ExceptionCode values in the <a href='https://developer.salesforce.com/docs/atlas.en-us.api.meta/api/sforce_api_calls_concepts_core_data_objects.htm#'>SOAP API Developer Guide</a>.
although I am giving lastname