Assign the value of a checkbox to a FormControlName (Angular)

I have a reactive form and want to take the value of a checkbox (not 'true' or 'false') and assign it to a formControlName (selectedSizeValueControl).

I have try some method but they do not work for me.

Can anyone please help?

The code:

<form [formGroup]="variantForm" (ngSubmit) = "submit()">

  <mat-checkbox value="" formControlName = "selectedSizeValueControl"  ></mat-checkbox>-->
 
  <mat-radio-button value=""><input type="text" #sale_preis formControlName ="sale_preis"></mat-radio-button>

  <button >save</button>
</form>