API error 400 error on tool_use

This is new to me, started the session a few times, slightly varied the prompt, after short while the same message.

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.4: `tool_use`

ids were found without `tool_result` blocks immediately after: toolu_01FzdpqJ1c5WXfRgAH3wCxxx. Each

`tool_use` block must have a corresponding `tool_result` block in the next

message."},"request_id":"req_011CTiQL9jTHWx2nUzyWUxxx"}