It is possible to add your VIABUY card to a PayPal account; however, PayPal will require that your card balance is at least 1.50 EURO, in order for them to be able to validate your card details.
Therefore, please make sure your VIABUY account balance is at least 1.50 EUR. PayPal will deduct this amount and then refund it once the card has been validated.
Alternatively, you can add your assigned IBAN as bank account to your PayPal account.
For further information on how to link a card to a PayPal account, please contact PayPal customer service directly.