When you select PayPal Business as the payment option on your invoice, your customers will be required to log in to a US-PayPal to make the payment for the invoice i.e. their country must be set to United States in their PayPal account.
Even though you have a PayPal Business account, you can select PayPal Standard as the payment option on the invoice creation page and your customers will be able to make payments using their credit cards.
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