Genesyscloud_flow update fails with 409 on conversation type change

Does anyone know how to resolve the 409 Conflict error when updating a flow’s conversation_type via Terraform?

provider: genesyscloud v1.68.4
region: au-1 byoc
resource: genesyscloud_flow

The state file shows the type changed from ‘voice’ to ‘chat’, but the API rejects the plan. Manual UI changes work fine. Is there a dependency lock I am missing in the HCL?