"Awaiting payment (unpaid)" status means that your customer has initiated a payment session but we haven't received the payment confirmation yet.

Either it's a slow payment method (like SEPA, BitPay or Multibanco) which takes up to 14 days to confirm, or some PayPal transactions stay in this state because you as the merchant have to go into your PayPal account to check if there's some manual approval needed (in case the payment is in a different currency than your PayPal account currency, for example).

After you approve there, it will become Paid in plug&paid automatically.

Other possibilities are that your customer abandoned their PayPal session, or there was some kind of error that did not allow the payment confirmation to go through.