pmpro-set-checkbox-group-defaults.php

<?php
/**
 * Set default values for specific checkbox group fields.
 * This function hooks into the fields before they're added to a form
 *
 * Set your checkbox group field names and default values in the $defaults array.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function my_pmpro_set_checkbox_group_defaults( $field ) {
	// Only modify checkbox_grouped fields.
	if ( is_object( $field ) && isset( $field->type ) && 'checkbox_grouped' === $field->type ) {

		// List of field names and their default values.
		$defaults = array(
			// Modify this array to match your specific checkbox group fields.
			// Format: 'field_name' => array('option1_value', 'option2_value').
			'checkbox_group_example' => array( 'cats', 'dogs' ),
		);

		// Check if this field is in our list of fields to modify.
		if ( isset( $field->name ) && array_key_exists( $field->name, $defaults ) ) {
			// Set the default values for this field.
			$field->default = $defaults[ $field->name ];
		}
	}

	return $field;
}
add_filter( 'pmpro_add_user_field', 'my_pmpro_set_checkbox_group_defaults', 10, 1 );