PayPal not showing "Guest Checkout"

I have WP Invoice installed and set up to use PayPal… However my clients do not see a “Guest Checkout” available from Paypal… They only see a “Log-in” Option. According to PayPal there should be a “Guest Checkout” option which would allow users to pay with a credit card without signing up for a PayPal Account. Am I doing something wrong? Thank you for you assistance.

https://www.ads-software.com/plugins/wp-invoice/