FBA refund question

Hi Recently started selling thru FBA, sold 20 unit in 4 days

Now I see that 2 customers got refunded. 1. Not delivered ( whatever this mean s) 2. Order not received.

In my mind, this is is fault of amazon delivery and it should not pay from my pocket.

As there is no information I can see on my selling central.

Is amazon paying for those refunds or am I?

Should I take action if they take money from my balance for the refunds?