Identify the bottleneck segment

NimbusCart's checkout request is taking far too long, and nobody can tell which service is responsible. Use the X-Ray service map explorer to investigate the slow request: read the nodes and look for the one glowing red, which marks the service carrying the highest latency.

Question: In the X-Ray service map, the API Gateway and Checkout nodes look healthy, but the Payment API node is glowing red with an average latency far higher than the others. Where is the bottleneck?