This is a great question, because it brings up several accounting issues at once.
First, the matching principle requires that the expense of stitching be recognized during the period when the finished inventory item is produced. In other words, when the article of clothing is manufactured (via a production order), the stitching cost must be included, because the full production cost of the item will be debited to Inventory on hand and incorporated into average cost of the inventory item.
Second, the definition of double-entry accounting requires the debit to Inventory on hand to be offset by a corresponding credit somewhere. In Manager, production order credits can only be posted to expense accounts, where they end up as contra entries. The reasoning behind that limitation is that non-inventory production costs transfer expenses that would otherwise be reported as expenses (and be debits in the larger scheme of things) to the Inventory on hand asset account. A simple example would be consumable supplies. You purchase needles for sewing machines and post their purchase to an expense account, Sewing supplies. On a production order, you enter a non-inventory cost with your estimate of the value of needles likely to be used up for the order. The resulting credit to Sewing supplies reduces the balance of that account and includes what was originally a debit there in the debit going to Inventory on hand. Labor is more complex, but the concept is the same. You would owe your tailor for the piecework even if you did not enter the production order. So a payslip would debit some expense account for the work, let’s call it Stitching expenses, while crediting Employee clearing account.
Third, as implied by the previous paragraph, paying the tailor is a separate transaction from stitching the clothing. Your liability for that is created by the payslip. And your actual payment is recorded by a payment at the end of the month. On the payslip, you would assign the stitching piecework to a payslip earnings item. When you set up that payslip item, you would designate it as posting to the expense account, Stiching expenses, mentioned above.
Now, from an accounting standpoint, it would also be correct to post the non-inventory cost on the production order to a liability account. After all, the contra entry to an expense account is the equivalent of a credit to a liability account. But that is unnecessary. By posting both the non-inventory cost on the production order and the piecework payslip earnings item to the same expense account, you avoid any need for a journal entry. You should be recording a payslip covering the stitching piecework during the same accounting period as the production order, so both position and performance will be properly reflected at the end of the period. (In fact, if you entered a payslip on the day the stitching was done, everything would be up to date at the end of the day, regardless of when your accounting period closed.)
The only reason you might want a separate liability account for the stitching piecework would be if you were not going to issue a payslip to the tailor until a future accounting period. In that case, the credit to the Stitching expense account would be artificially reducing your real expenses. But doing that would violate the matching principle by itself, as the debit from the tailor’s labor would be delayed from the accounting period during which it was incurred. And that would artificially increase your net income, not a good result either.
As a final note, I admit there are some circumstances where posting non-inventory production costs to a liability account might be appropriate without violating any accounting principles. But I have a hard time thinking what they might be. And production of clothing does not seem to be one, because all operations are going to be completed in short time frames.