What are common issues with form actions in PHP, specifically related to checkboxes not being processed in the POST string?

Common issues with form actions in PHP related to checkboxes not being processed in the POST string can occur when checkboxes are not checked, resulting in their values not being included in the POST data. To solve this issue, you can use isset() function to check if the checkbox is checked and assign a default value if it's not present in the POST data.

// Check if the checkbox is checked and assign a default value
$checkbox_value = isset($_POST['checkbox_name']) ? $_POST['checkbox_name'] : '0';