"Error establishing database connection" in subdirectory

I am following this tutorial for three WordPress sites: https://www.digitalocean.com/community/tutorials/how-to-install-wordpress-on-ubuntu-20-04-with-a-lamp-stack

The first two were set up with no issues. The third, however, is in a subdirectory. I tested that there is a connection with mysql -u <DB_USER> -p<DB_PASSWORD> -h <DB_HOST> <DB_NAME> I also tested that it is reading my wp-config.php by adding die(“Loading this file now”); to the top. So it does display that line now. I also looked at How To Debug the WordPress “Error Establishing Database Connection” https://www.digitalocean.com/community/tutorials/how-to-debug-the-wordpress-error-establishing-database-connection but none of those suggestions helped.

I am thinking it is perhaps related to the fact that I putting WordPress in a subdirectory: mydomain.com/blog Maybe some permission issue?

Any ideas?