[b6z]

That sounds too negative. How about that:

"The prize-winning Excel service is in high demand right now. We apologize for any delay this might cause. Do you want to become an 'Excel Prime Plus User' with preferential treatment? Just upgrade your subscription now and increase your productivity!"

[southwesterly]

“I’m sorry, in order to multiply you will have to purchase a subscription to our multiplication extension. Please click HERE to have your credit checked.”