If your customer already has his own OkiOki account (which he pays for himself or because he is with another OkiOki accountant and is now switching to you), you can link his OkiOki account with your OkiOki portal.
You do this by entering the VAT number in a new customer profile. As soon as you do this, OkiOki will recognize the VAT number and ask if she can send your customer an invitation to link their OkiOki account with your accountancy.
Once the customer has confirmed this, this customer will appear in your list of active customers and you will have access to their OkiOki account. Then you can also configure the UBL or Coda transfer settings, for example.