PayPal Credit is not like a regular credit card account which you can use on demand. Just because you have a PayPal Credit account is no guarantee that you can use it when you want. PayPal evaluates each potential purchase to determine if qualifications are met for that purchase. If they are met you will have the option to use PPC. If not, then just chose another payment method such as a credit card.
All you can do now is maintain an excellent credit score, low debt to available credit with credit cards, good financial basis, no PayPal disputes, no PayPal issues, and other financial and risk factors.
