If you have issued an incorrect invoice (an incorrect amount / payment method, etc.) and it has already been send to the EET, do not worry; you do not have to delete the entire document. All you have to do is open the existing document in edit mode and make the correction.
After saving the modified document, the original transaction is automatically cancelled in the EET and the new transaction amount is submitted.
This function saves you from breaking the invoice/receipt sequence, which can happen when documents are deleted.
Cancellation in EET can be also done while deleting the document. You will be asked if you want to cancel the revenue in EET altogether with erasing the document.
Last option is in document editation. In the lower part of the editation you can see Cancel button. This button will just cancel the revenue send to EET, document will remain in your profile.