You were lucky with PayPal that time but others have had their accounts closed when they find out its firearms related. And they class airguns as firearms
From BAR's website
PLEASE NOTE:
DUE TO PAYPAL POLICIES, WE ARE UNABLE TO ACCEPT PAYPAL AS A PAYMENT METHOD FOR THE PURCHASE OF ANY AIR RIFLE, PISTOL OR SILENCER
THESE ITEMS CAN BE PURCHASED ONLINE VIA CREDIT/DEBIT CARD OR BANK TRANSFER