Add A Default Campaign Custom Amount

add_filter( 'charitable_session_donation_amount', 'example_get_donation_amount_in_session', 999, 2 );

function example_get_donation_amount_in_session( $amount = false, $campaign = false ) {

	// If the donation amount is not set in the session, return the default amount.

	// WARNING: Setting a default amount here will override any default amounts that might be set in the Charitable settings.

	// ALSO NOTE: This will only work for donations made via the donation form. It will not work for donations made via the admin.

	// FINALLY: Setting a default amount for the user can be a bad idea, as it can lead to accidental donation amounts.

	if ( ! $amount ) {

		return 100;

	}

	// Otherwise, return the amount.

	return $amount;

}