Bulk Discount Now gives shoppers discounts through Shopify's Draft Orders feature. Shoppers go through checkout for a draft order which works a bit differently from the normal checkout of a cart.

To pay via Paypal Express and still get their discounts, shoppers would need to click the Paypal button after they enter the checkout. If they click the Paypal button on the cart page, they wouldn't receive their discounts.

We recommend hiding the Paypal button on your cart page (but keeping it on the checkout page) to prevent any issues.