> For the complete documentation index, see [llms.txt](https://help.tahua.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.tahua.io/knowledge-base/integrations-help-guides/xero/xero-faqs/syncing-milestone-errors/lock-dates-and-xero-syncing.md).

# Lock Dates and Xero Syncing

**Overview**

A lock date in Xero prevents changes from being made to transactions in a past period. This is commonly used by finance teams to close off a period once reconciliation is complete.

* Set a lock date to stop changes being made to transactions during a past period.
* You can change and remove the lock date at any time.

For more information on setting up lock dates in Xero, visit: <https://central.xero.com/s/article/Set-up-and-work-with-lock-dates>

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**How lock dates affect Tahua**

When Tahua attempts to sync a milestone to Xero as a bill, the bill date is usually set to the contract start date. If that date falls within a locked period in Xero, the sync will fail.

When this happens, you will receive an email to your configured sync error address. The email will include links to the relevant Milestone, Application, Contract, and Xero Bill to help you investigate.

***

**Resolving a lock date sync error**

You have two options:

1. **Unlock the period in Xero** — update or remove the lock date in Xero so that the bill date is no longer restricted, then use the resync link in the error email to retry.
2. **Choose a different bill date** — when manually resyncing a milestone from Tahua, you can select a different bill date that falls outside the locked period.

Remember: You can exempt a Milestone from syncing through to Xero by following [these steps](/knowledge-base/integrations-help-guides/xero/xero-faqs/syncing-milestone-errors.md).