The delete action can be looked up in the journal table.
In the case of a cloud instance, we can look up the data for you as a custom service, where it is possible to check whether a DELETE action was performed on any record in the invoice register within a given period; however, the document cannot be restored.
In the case of your own server or a local installation, a backup needs to be provided to the company (you can upload it at https://www.flexibee.eu/nahrat/), in which we can then look up the data in a similar manner as described above.