Sometimes an order is in a payout before its payment is. The payment can arrive in a later payout. The order then appears in an earlier payout than the money for it.
This can happen for a number of reasons. Two of the most common are:
The order is paid after it is fulfilled (for example credit terms or cash on delivery).
The order is made through one gateway but paid through another (for example because a payment through the first gateway failed).
In these cases Taxomate adds a Pending Payments line to the payout. The line goes to the account Shopify Pending Balances. It stands for money that is still owed for the order. The line reverses when the payment arrives.
You choose the account for Pending Payments on Accounts and taxes. See "What are Accounts and taxes?".
Shopify explains pending payments here: Shopify Help Center: pending payments.