marriot Bonvoy Credit card

As we were in a tentative purchase, we needed another credit Card. They offered us the Marriot Bonvoy Card, which we found out later has an annual rate of $450. $300 were waived because of the pending purchase, which left us with many Points 90,000, BUT one has to spend $5,000 in 3 months in order to Keep these Points. Hmm is that all above board ?

Yes. Just about every CC associated with a rewards program has a minimum purchase to qualify for the bonus. Read the fine print when you're handed an application on a flight, for example. You can easily spend $5000 in 3 months by charging EVERYTHING including groceries, gas, utilities and any other regular payments to your CC. Did you ask if you can charge part of your purchase on the new card? I've bought Marriott timeshares by charging to my Marriott card and getting 5x points.