An invoice from December 2018 is showing up in 2019 because it was paid in January via interac transfer. The transfer amount is showing up as a negative but being added.

Hi Zéroperte,

Making sure all your invoices and payments are recorded accurately is the best way too unlock the full potential of QuickBooks Online's powerful tracking for your accounts receivable. You'll always know exactly how much you're owed, while gaining clear insight into the aging of each invoice. You can easily match a payment from the bank feed to your existing invoice. I'll be glad to help with this.

Interac e-Transfers typically include the word "transfer" in the description, which QuickBooks Online uses to estimate how the transaction should be categorized. If you see Transfer as the suggestion, you can disregard that. Simply click anywhere else on the transaction then select Find match to search for the specific invoice. You may need to update your date filters if you can't see the invoice. This'll automatically mark your invoice as paid.

Hope this helps! I'm here if you have any more questions.