Hi @Zoe14 ,
Have you seen multiple issues of this in your store? You can refer to the abandoned checkouts section of your Shopify admin to see if other customers have had PayPal issues at checkout. If not, it’s more likely to be an issue on the customer’s end. If you want to be sure of this, I would recommend speaking to PayPal directly as they can offer more insight any failed attempts to process a payment via their gateway.
Kind regards,
Victor | Shopify Social Care