Enter or change the tax number or tax identification number in the master data for using the Internet Export Declaration Plus (IAA Plus).
Source: Serviceportal Rheinland-Pfalz
If you wish to declare goods for export from the customs territory of the Community using the IAA Plus, you must first authenticate yourself with an ELSTER certificate. The tax number or tax identification number (tax ID) on which the ELSTER certificate used for the declaration is based must be stored in the master data stored for your EORI number (Economic Operators Registration and Identification number).
In order to enter a new tax number or tax ID in the master data or to change the entry, for example because you made a typing error when entering the master data for the first time and therefore a registration in the IAA Plus is not successful, you must submit an application to the master data management of the General Customs Directorate by fax only.