Button icon is not showing when I use xml drawable on api 19

[bugloos]

Here is my code:
<mehdi.sakout.fancybuttons.FancyButton android:id="@+id/btn_facebook" android:layout_width="0dp" android:layout_height="48dp" android:layout_marginEnd="16dp" android:layout_marginTop="24dp" android:paddingBottom="10dp" android:paddingTop="10dp" app:layout_constraintDimensionRatio="w,1:1" app:layout_constraintEnd_toStartOf="@+id/guideline" app:layout_constraintTop_toBottomOf="@+id/textView" fancy:fb_borderWidth="1dp" fancy:fb_defaultColor="#3b5998" fancy:fb_focusColor="#5577bd" fancy:fb_fontIconSize="25sp" fancy:fb_iconPosition="right" fancy:fb_iconResource="@drawable/facebook_f" fancy:fb_radius="5dp" fancy:fb_text="" fancy:fb_textColor="#FFFFFF" />
and here is fb_iconResource source:
`

<path
    android:fillColor="#ffffff"
    android:pathData="M76.7 512V283H0v-91h76.7v-71.7C76.7 42.4 124.3 0 193.8 0c33.3 0 61.9 2.5 70.2 3.6V85h-48.2c-37.8 0-45.1 18-45.1 44.3V192H256l-11.7 91h-73.6v229" />

`

its working well on api 21+.