Unable to connect to Managed Postgres from a Function

I have a managed Postgres database and an App that currently just contains a Function written in Node.

I have added my App and my local IP as trusted sources to my database.

I can query the database from my computer, but the exact same code times out when connecting to the database when running in both the Sandbox and Production Function environments.

This works:

const pool = new Pool({
    connectionTimeoutMillis: parseInt(process.env.PGCONTIMEOUT),
    user: process.env.PGUSER,
    host: process.env.PGHOST,
    database: process.env.PGDATABASE,
    password: process.env.PGPASSWORD,
    port: parseInt(process.env.PGPORT),
    ssl: {
        ca: process.env.CA_CERT
    },
});

let failure = null;

const response = await pool.query('SELECT test_column FROM mrspeaker.mrspeaker.test')
            .catch(reason => failure = reason);
await pool.end();

const actual = failure === null ? response.rows[0].test_column : failure.toString();

expect(actual).toEqual(595);

The exact same code (replacing the assertion with return actual;) running in the function sandbox just returns Error: Connection terminated due to connection timeout.

If I remove all trusted sources from the database I get the same result.

My project.yml:

targetNamespace: ''
parameters: {}
packages:
  - name: mrspeaker
    actions:
      - name: main
        runtime: 'nodejs:default'
      - name: hello
        runtime: 'nodejs:default'
environment:
  BOT_TOKEN: ${BOT_TOKEN}
  PGHOST: ${PGHOST}
  PGPORT: ${PGPORT}
  PGUSER: ${PGUSER}
  PGPASSWORD: ${PGPASSWORD}
  PGDATABASE: ${PGDATABASE}
  PGCONTIMEOUT: ${PGCONTIMEOUT}
  CA_CERT: ${CA_CERT}

My deploy command for the sandbox: doctl sandbox deploy . --env .env

My .env file with values removed:

BOT_TOKEN=

PGHOST=
PGPORT=
PGCONTIMEOUT=
PGDATABASE=
PGUSER=
PGPASSWORD=
CA_CERT=

Am I totally misunderstanding something or am I just missing a small detail? Any help would be greatly appreciated!