Hey there Kairlm! I understand you are having some issues using PayPal on the Marketplace. Do you have issues purchasing multiple things with PayPal? Are you able to purchase using a different payment method entirely?
Also, please refer to our Payment Method guide (forums.xbox.com/.../153161.aspx) to ensure that your PayPal account meets all the criteria for use with Xbox LIVE. Please let me know how that goes, thanks!