If the number is not in your name, you require an authorisation to order the service. To obtain it, contact the owner of the number.
If your phone number belongs to a company and you want to register the MultiSIM service to the company invoice, you need the authorisation of the owner of the number, or the owner of the number must allow ordering the MultiSIM service on behalf of the company. For this, an authorised representative of the company must contact Telia.
If you wish, you can also conclude the MultiSIM service as a private person; in this case, no authorisation is required. For this, you need to join the Private Invoice service and formalise the MultiSIM service monthly fee to the Private Invoice.