503 error showing on EC2 instance after reboot

I need help with an issue related to my company's Conversions API Gateway on AWS EC2. After logging in successfully, I encountered a white screen on the dashboard and a 400 error in the console log. I tried rebooting the instance, but now I'm facing a "503 Service Temporarily Unavailable" error. I'm new to AWS and have researched troubleshooting methods, but I'm still stuck. I couldn't find any relevant errors in the CloudWatch logs, and when I checked the error.log file through EC2 Instance Connect, it was missing from the var/error/nginx/ folder.