The promotions are for both eBay and PayPal. Plus, they tend to run other promotions such as earning specific X amount of rewards for using the card for other MC purchases.
Ok, now as far as the PayPal credit application, wait for the letter because if your PayPal Extras MC is linked to that PayPal account then that would be a no-go (can only have one per product). Call me crazy but I have all 3 (PayPal Extras MC, eBay MC and PayPal Credit - the eBay MC was a SYNCB screw up that worked in my favor
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Perhaps someone who had a similar experience with the PayPal Credit denial can chime in. Can't recall if there's a number that one could call to rectify the mix up so you can provide them with a separate PayPal account to link (assuming this might be the issue).