I don't have enough credit on my credit card to cover the whole amount of my purchase. Can I still take out a plan?

Unfortunately not.

You need to have at least the whole value of your purchase available on your card as an authorization (hold) is kept on the total amount outstanding in oredr to guarantee future payments to your merchant or retailer.

The authorization amount reduces with each monthly payment you make until the balance is cleared and are renewed periodically. The previous authorization is removed as soon as a new one is obtained.