This visual execution shows how a REST API server creates and sends a Problem Details JSON response following RFC 7807 when an error occurs. The server detects an error, then builds a JSON object step-by-step adding fields: 'type' as a URI to identify the error type, 'title' as a short human-readable summary, 'status' as the HTTP status code, 'detail' with a detailed explanation, and 'instance' as a URI pointing to the specific error occurrence. The client receives this JSON and can read these fields to understand and handle the error properly. Key points include the use of URIs for 'type' and 'instance' to uniquely identify errors and occurrences, and matching 'status' to the HTTP code. The execution table traces each step of building the JSON, and the variable tracker shows how each field is added. The quiz questions check understanding of field values and their creation steps.