invalid vendor account

[Muhammadbutt000]

Hello, team
We are facing an issue regarding our checkout page. When we click on Paypal payment method the massage pop up and state that invalid vendor account. we have change and try every setting in our Paypal API setup. we are diagnosing this issue from last week. but unable to find a solution. 
can you please look in to it, 
the store URL is:  https://welcomebypet.com/

Looking forward to hearing from your side. 

Regards, 
Muhammad Butt
Welcomebypet.com