There are a number of reasons why a voucher may not be accepted.
 
To successfully use a voucher, be sure of the following:

• You use the same email address for both eBay and PayPal accounts
• You've confirmed your email address
• The voucher you received was sent to your confirmed email address used for both accounts (if the voucher was received by email)
• The minimum amount required was met
• Only one voucher is allowed per single item purchased
• The item should be listed on eBay.co.uk
• The voucher has not expired. The expiry date is stated on the voucher.