curl --request GET \
  --url https://api.app.lastaccountingcompany.com/portal/invoice-customers \
  --header 'Authorization: Bearer <token>'

{
  "customer_id": "<string>",
  "customers": [
    {
      "name": "<string>",
      "id": "<string>",
      "business_id": "<string>",
      "vat_number": "<string>",
      "address_line1": "<string>",
      "postal_code": "<string>",
      "city": "<string>",
      "country_code": "<string>",
      "email": "<string>",
      "einvoice_address": "<string>",
      "einvoice_operator": "<string>",
      "default_payment_terms_days": 123,
      "default_vat_code": "<string>",
      "default_vat_rate_basis_points": 123,
      "default_invoice_language": "<string>"
    }
  ]
}