For your security, T-Rex requires a password that is secure enough. T-Rex requires customers to use highly secure passwords, avoiding the use of commonly used character strings.
Placing restrictions on customer passwords prevents brute force attacks where passwords of different character sequences are randomly checked for an ID or attacks dictionary in which pre-existing passwords in the dictionary are randomly checked. There is also something called an account list attack where ID and password combinations are stolen from a web service and used in an attack. Please note that the same ID and password should never be used across multiple services.