We released a fix today for the issue that occurred in Safari with the Payjunction payment form. Due to the limitations of the form, a client's browser is required to allow third party cookies. Safari's default cookie settings are configured to "Allow cookies from websites I've visited". This setting was preventing the form from loading for Safari users (they instead saw an error message that read "The QuickShop store you tried to access is invalid"). This error did not occur in other browsers like Firefox or Chrome because the default cookie settings in these browsers allow third party cookies.
To resolve the issue, we are now loading the PayJunction payment form in it's own browser tab when a client clicks the "Make A Payment" button on an invoice. The payment form should function properly now in all browsers regardless of the user's cookie settings (unless they have configured their browser to block All cookies).
If you have any questions regarding this issue, please feel free to contact our support team at 888-974-6687 (M-F 8am-5pm PDT) or submit a support form.