Imaam pausing in the middle of the khutbah to make an announcement

Q: During the Jumu'ah Khutbah (the second Khutbah) the Imaam stopped in the middle of the Khutbah and made an announcement saying "whilst the Khutbah is on we are not allowed to talk". 

1. What is the ruling, will this nullify the Khutbah or not? 

2. What is the ruling with regarding to stopping the Khutbah to make an announcement? 

3. Will the Jumu'ah have to be made Qadha of?

Selling items on online stores with different payment options

Q: On Amazon and other online stores, there's a type of installment payment that involves interest. The buyer takes out a loan from the bank to pay for the product in installments, and the store pays the seller upfront without any interest. The buyer pays the installment to the store, and the store pays the seller the full price of the product immediately. 

It's not possible to disable this payment option on these stores. 

Would it be legal to sell on these online stores?