This happens sometimes if the payment processor that your Recur360 account is connected to has an interim outage when we are sending payment requests to them. If this error shows in your Invoice Errors report then Recur360 was unable to process the payment at the time we generated and emailed out invoices.
Go into the Invoice Errors report and look for any transactions with that full message, then manually click to Process Payment and attempt to process again and it should go through assuming there still isn't an outage.