Paypal payments not received

Hi, I’m at a loss and don’t know what to do. For the last couple of months, payments with paypal on our website have been failing, on and off. Customers report entering their paypal details to pay and being taken back to the checkout/billing page of our website. We receive their order but not their payment. I have looked everywhere and cannot fix it. I have spoken to Paypal who said it’s not them, all their systems are operational. Could you please help? Thank you so much ??

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