Nexonia can be configured to prevent users from adding more items to an expense report once all items in the report have been Submitted for approval.
To prevent this, click Settings > Company > Features > Edit. Scroll down to the expenses section and check the box next too "Prevent adding entries to a report once all entries have been submitted". Then scroll to the bottom of the page and click apply.
Going forward, users will not be able to add items to a report after all items in the report have been Submitted.
If users needs to have the ability to recall expenses because they submitted prematurely or need to make changes, an Administrator can enable the Recall function. Refer to the article "Allowing Users to Recall Submitted Expenses" for more details.