An example of gform_validation where we validate a field value based on a minimum value from a custom metabox

gform_validation

/**
 * Custom validation so that a bid less than the minimum custom metabox is not allowed
 *
 * @since   0.1.0
 *
 */
add_filter( "gform_field_validation_10_1", "min_bid_validation", 10, 4 );
function min_bid_validation( $result, $value, $form, $field ){
    
    // Get the correct output from the form
	$id = rgpost("input_3");

    // Get the correct minimum bid out of a CMB & make sure it's a proper integer'
	$min_bid = get_post_meta( $id, 'cmb_auction_min_bid', true );
	$min_bid = intval(str_replace( ",", "", $min_bid ) );

    // If the value from our field is less then the minimum bid, return false * give the user a reason.
    if($result["is_valid"] && intval($value) < $min_bid){
        $result["is_valid"] = false;
        $result["message"] = "Please enter a value higher than the minimum bid (Minimum Bid on this auction is $$min_bid)";
    }
    return $result;
}