Webserver can't connect to Remote Database using Private IP

I’m trying to connect my web server (planning to run Wordpress) to my remote database server on a private network, both hosted on Digital Ocean.

I’m currently using Runcloud.io to install LEMP on my servers.

The issue I’m facing is, I can get private networking running fine:

1. I can ping my DB server’s private IP
2. Running nc -zv private_ip 3306 is successful
3. Running mysql -u username -p -h public_ip is successful

Yet when I try connect to mysql (from my web server) using my private ip, I get the following output:

ERROR 1130 (HY000): Host 'webserver_private_ip' is not allowed to connect to this MariaDB server

I set up my private networking using this guide: https://www.digitalocean.com/community/tutorials/how-to-enable-digitalocean-private-networking-on-existing-droplets

Any help in this is greatly appreciated