US vat on my commision

I’m still confused about the varying value of the vat on my 29$ tracks,
sometimes I gain 7.25$ and today some track of mine was sold and I gained 3.75$ which is pretty odd,
how is that?

Are all those tracks from EEUU?

Yes United States

The only one thing that i could say is… Is there a change in the taxes between your country and EEUU lately? And that is the reason…?
Because in the same conditions that is the only one i could suppose.

Or, directly ask to help center they are the best to resolve this.