Why is a 'Non-refundable deposits' from customer contracts a Liability?

And sir what would Non-refundable payments be?
This is a bpp kit question:

“Blochberger is a manufacturer of consumer goods. On 30 November 20X7, Blochberger entered into a one-year contract to sell goods to a large global chain of retail stores. The customer committed to buy at least $30million of products over the one-year contract. The contract required Blochberger to make a non-refundable payment of $3 million to the customer at the inception of the contract. The $3 million payment is to compensate the customer for the changes required to its shelving to accommodate Blochberger’s products. Blochberger duly paid this $3 million to the customer on 30 November 20X7. In December 20X7, Blochberger transferred goods to the customer worth $4 million to the Customer and invoiced them for this amount. “

sir, what will be the accounting treatment of Non refundable advance (example $ 300)

if goods are supplied in the same Financial year & half payment is received immediately (example $ 400), balance(Example $ 500 ) will received next Financial year.

Thanks