How to solve the problem with user rights to set up database replication?

Question

MySQL

Good day.

There was such a problem when setting up database replication - it is not possible to give the user rights. The user is created, granting permissions with GRANT REPLICATION SLAVE ON *.* TO 'slave_user'@'%' IDENTIFIED BY 'password'; login and password I enter, respectively, the desired user. As a result, the inscription appears: Query OK, 0 rows affected, 1 warning (0.00 sec) and nothing more. What could be the problem? How can I find out what this warning is?

Thanks in advance.