How do I know when my 100$ search ads promo credit is exhausted? In Apple's terms for Search Ads Promo Credit thay say that you will not be notified. I currently have 30$ which I am spending on ads. But I also have the 100$ promo credit. I currently have only spent 20$ worth of ads. 

So how do I know when my promo credit is being applied? Will I just have to do the math until 130$ is spent? Or will there be something which indicates for example if I am currently spending promo credit?
I don't think there's a specific way to know.  I have the promo $100, too, and I was looking into this.

The only way I found out was to check on the available balance every few weeks.  Even doing that, you have to accept that you might go over the promo amount.  Of course, this is exactly what Apple is hoping will happen (in my personal opinion; I don't have any proof for that).