My invoice was marked as paid, where are the funds? 

With Invoices, the only payment method that we know for certain if your client has paid is if you enabled the card payment option and they pay via a card. 

When a client views the Invoice they are able to click and mark if they paid the Invoice and you'll get a push notification, but this is simply the client reporting that they paid. 

With the other payment options (bank transfer, payment apps, etc.) the actual payment of the Invoice all happens through the external account (either the client's bank, or the relevant payment app), we can't know for certain if the client has actually paid until you actually receive the payment. 

If your client has marked that they paid the Invoice and you haven’t yet received the payment within a few business days, it’s best to reach out to the client to confirm when and how they initiated the payment and if they can provide any receipt or confirmation of the transfer they say was initiated.