This error comes from the use of Array without any type for the elements in the array. To solve this error, define a type for the contents of the array. You can define this in 2 different ways:

Solution 1:

clients: String[];

Solution 2:

clients: Array<String>;

If the type of the array can’t be determined, use any:

any[]
Array<any>

Note: Using the T[] syntax is recommended over Array<T> syntax