PayPal Holdings, Inc. Prepaid Card Complaint

PayPal Holdings, Inc. Prepaid card department,

Mobile wallet New Mexico

In the process of making a purchase over the internet through a small business commerce site I signed up for Paypal yet did not clearly understand that I had to use a credit line for the purchase. I was contacted by a collection service to pay off the remaining balance which I did during that phone call. Looking back at the process I would like to know if the extremely high interest rate I paid for the lats month of the credit line was actually legal?