This happened due to MySQL Validate Password Policy level is higher.
You can see password validate configuration metrics using the following query in MySQL client:
SHOW VARIABLES LIKE 'validate_password%';
The output should be something like that :
+--------------------------------------+-------+
| Variable_name | Value |
+--------------------------------------+-------+
| validate_password.check_user_name | ON |
| validate_password.dictionary_file | |
| validate_password.length | 6 |
| validate_password.mixed_case_count | 1 |
| validate_password.number_count | 1 |
| validate_password.policy | LOW |
| validate_password.special_char_count | 1 |
+--------------------------------------+-------+
then you can set the password policy level lower, for example:
mysql> SET GLOBAL validate_password.policy = LOW;
What do you think?