There is this statement in the PP Help Center:
"PayPal generally prohibits transactions for all types of tobacco products, including cigarettes, cigars, and smokeless tobacco due to legal requirements and industry regulations for online tobacco sales."
Any merchant selling these products and offering PP is either doing so without PP's knowledge or with written permission. That permission can be revoked by PP at any time, for any reason, without explanation, and without recourse by the merchant.
My state in the USA now considers e-liquid the same as a tobacco product - yours may not, but it is a very slippery area right now.
Edit-: seems All ecig products are banned for EU through paypal now