this.mainForm = this.formBuilder.group({
          productType1: new FormArray([], CustomValidators.minSelectedCheckboxes()),
          productType2: new FormArray([],CustomValidators.minSelectedCheckboxes()),
        });
      }

static minSelectedCheckboxes(min: number = 1): ValidatorFn {
    const result = (formArray: FormArray): { [key: string]: boolean } | null => {
      const totalSelected = formArray.controls
        // get a list of checkbox values (boolean)
        .map((control) => control.value)
        // total up the number of checked checkboxes
        .reduce((prev, next) => next ? prev + next : prev, 0);
      // if the total is not greater than the minimum, return the error message
      return totalSelected >= min ? null : { required: true };
    };
    return result;
  }