create_user INT UNSIGNED ZEROFILL cannot reference id INT, because these count as different data types for purposes of foreign key reference. Make them the same data type.
The only data type difference that is permitted between columns in a foreign key relationship is length of a varchar. For example, VARCHAR(10) can reference VARCHAR(20) or vice-versa.
Any other difference in data type, size, or character set is incompatible for referential integrity.
Even having ZEROFILL on one column but not the other makes the data types incompatible.