Answer: The total price of the first invoice that activates the chain discount is $1040.40.
Step-by-step explanation: The chain discount of 20/15 means that there are two successive discounts: first a 20% discount and then an additional 15% discount. These discounts apply when the invoice subtotal is above $1,000.
Therefore, the total price of the first invoice that activates the chain discount is $1040.40.