If checked, the Approve checkbox, first of all confirms billable issue and the entire service order. With this the current date is entered in billable issue as invoice date. Moreover:

• billable issue is marked as approved
• service order or service receipt is marked as approved
• service issue is marked as approved and the current date is entered as invoice date (this information of a lesser importance in service orders since this issues do not belong to VAT records)

Before continuing you have to confirm the operation.

Clicking  performs all the above-mentioned operations. Becasue document approval also represents changing the date of invoice decisive in providing correct VAT records, you are unable to approve the already approved document and error is returned (see Document already approved! It cannot be approved anymore!). If you still want to change data in billable issue, you can do this directly in the document.

Cancel the operation clicking .