PayPal Credit not available when using PayPal for iMac purchase

I've been trying for days to use my PayPal Credit account to purchase my new iMac (online, and through the iPhone "Apple Store" app), but every time I select PayPal as my payment choice and click to proceed (and am then transferred to my PayPal account to select which bank/debit/cc account I want to use as the specific payment method, every bank and credit-card funding source is available to select except PayPal Credit. That account is nowhere to be seen. Any ideas on how I can solve this problem? Is PayPal Credit not usable for Apple "hardware" purchases?

Thank you (and I apologize for the long-winded question).