Payment can not be successful for many reasons, which may include:

For credit card payment cases:

1) Failed to pass PayPal security requirement
Solution -> Please call PayPal and seek help (Customer Service Hotline for "PayPal Hong Kong" account holder: Tel :3550 -8574 / 3002-1220 )

2) Failed to pass the credit card company (Bank) security requirement
Solution -> please call the bank and seek assistance

3) Your credit card's online shopping function not yet activated.
Solution -> Please contact your bank to activate

4) Credit limit
In general, each credit card spending limit can be cumulated to HKD25, 000 (sum up all previous spending).
Solution ---> login to your PayPal account, click "get verified" in the homepage >>  Click "Link my card" >>  (input the 4-digit PayPal code) .After confirmation, the payment limit would be canceled.
 

Note: While verify your Credit Card, PayPal will charge this card $15.00 HKD or equivalent to make sure it's yours. PayPal will refund the money into your PayPal account within 24 hours after you confirm your card.

The other reason of the limit problem maybe due to you required your credit card company to set a limit for online shopping.
Solution -> please contact your bank, as opposed to increase your limit proposed

For PayPal Balance settlement case:
 

1. You will not yet verify your PayPal account (New account holder)
   Solution －－＞Check your email box to find the verify email from PayPal and verify your account
    
2. Your PayPal Balance amount is insufficient
   Solution －－＞Top up your account