Cannot connect to AWS RDS database from EC2 server

I am attempting to connect and perform migrations to a newly created RDS database from an EC2 server. I have verified that both resources are currently within the same VPC and they are connected via a custom security group that I created by utilizing the "Set up EC2 Connection" feature within the RDS screen.

The "odd" part of the issue is that I can perform the necessary database migrations opening an SSh connection and running php artisan migrate --force manually. However I attempt to utilize any kind of automation, like the Laravel Forge "Deploy Now" button, it will fail and say that the credentials are incorrect.

Is there something that I am missing?