What are common errors when setting up a newsletter addon in PHP?

Common errors when setting up a newsletter addon in PHP include incorrect database connection details, missing required PHP extensions, and improper file permissions. To solve these issues, ensure that the database connection details in the configuration file are correct, install any missing PHP extensions using a package manager like Composer, and set appropriate file permissions for files that need to be written to.

// Example code for connecting to a database in PHP
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "newsletter_db";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);

// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}