Data table issue - ERROR TypeError: val.slice is not a function

ERROR TypeError:

val.slice is not a function

dataTable configuration

$.p-dataTable #dt [value]="customers" [(selection)]="chkBoxSelect" 
 dataKey="customerId" [rows]="10" [paginator]="true" 
 paginatorPosition="both" [pageLinks]="5" [rowsPerPageOptions]="[5,10,20]" 
 [globalFilter]="gb" [headerCheckboxToggleAllPages]="false" 
 [editable]="true" exportFilename="customers" [lazy]="true" 
 [totalRecords]="totalRecords" onLazyLoad)="loadCustomersByPage($event)"

Call back function

$loadCustomersByPage(event: LazyLoadEvent) {

    const parameters = "?page=" + event.first + "&size=" + (event.first + event.rows);

     this._cs.findAllActiveCustomerDetailsByPage(parameters).subscribe(
       (data: any) => {
         this.customers = data;
       },
       (error) => {
          console.log("--error--" + error)
       }
  );
}