The packet capture shows that the packets are arriving at Server B and that the server responds, indicating that Server B is reachable and the API service is running. However, since the developer cannot access the API, the most likely cause is that the return traffic on port 443 (HTTPS) is being blocked on the incoming interface of Firewall B. This means that although Server B is responding, the responses are not getting back to the developer's client because they are being blocked by the firewall.