PayPal uses various security measures to protect their users. Because of this, PayPal may occasionally prohibit a buyer from submitting payment to a seller through PayPal.
Contact PayPal's customer service team for help and learn more in their Security Centre.
If you're ultimately unable to submit payment, try working with the seller to determine an alternative payment method. Learn how to contact a seller.
If the seller accepts credit cards directly on Etsy, you may be able to purchase with your credit card.