AWS expert to config the webapp, SSL certificate, RDS

I am looking for an experienced AWS expert to complete the configuration of my custom-built webapp as soon as possible. I have an EC2 instance (Windows) that I have been running a webApp (Angular) over ng serve. The webserver is accessible through the public IP of the instance. The database is over RDS; however, the webapp cannot communicate with the RDS (the API connectivity of OK through test tool). I also had my databse on Xampp but through public IP of the instance was not accessible. I reconfigured the security setting but still does not work. I tried to get SSL certificate for the domain but I don't know why the certificate was rejected whereas the domain is transferred to AWS.
There should be a simple configuration that I am missing. So, I need someone to guide me how fix it.