Error: The document date cannot be before the period lock date
Another error message with the same cause and solution looks like this:
This error comes up when an expense (or expenses) has a presentment date that falls within a locked period. This can happen when:
The Pleo expense was not exported in time (i.e., before the books were closed for the respective timeframe).
There is a discrepancy between the UTC timestamp of presentments versus the date of the purchase in your timezone. For example, a presentment from May 31st at 23:30 should go into the May books in Xero. However, Pleo will have stamped it as June 1st.
Log into Xero and open the books for the specific date range (under Accounting - Advanced - Financial settings).