I have had reports of clients being unable to pay via paypal via the checkout, but they can pay invoices via client area
I have tested this out myself and I can confirm its very odd.
All settings are fine within Paypal and whmcs settings from what I can tell, the api credentials are correct
basically you can go through the whole process of selecting the product, and addons etc. you choose from diff payment options like credit card, paypal, alertpay etc
you select paypal, click checkout
you get a blank page, url in the address boxes is
https://www.domain.com/cart.php?a=checkout
it never goes past this, but it will create an invoice, where they can go into their account and choose to pay.
what is the issue?