Which SSL-certificate can insure a secure TCP-connection between C# listener on Amazon Lightsail instance and iOS app?

I created a simple .NET Core Console application on C# which uses TcpListener to accept connections on a specific port and return an answer.

I bought an AWS Lightsail instance and deploy my server application manually via RDP. The instance has a static IP-address and a domain name like ec2-<IP>.eu-central-1.compute.amazonaws.com (as I discovered via reverse DNS lookup). The client is an iOS application and it needs a secure TCP connection to transfer data to server and vice versa. iOS app is not working with my self-signed certificate - it needs to use certificate from trusted CA, so the question is: where I can get the trusted SSL-certificate for Amazon Lightsail instance mentioned above?