Extra keys warning for dynamically generated data

const customerOutputFields = (z, bundle) => {
  const response = z.request(
    "https://app.zenmaid.com/api/zapier/v1/customers/custom_field_definitions"
  );
  // json is like [{"key":"field_1","label":"Label for Custom Field"}]
  return response.then((res) => res.json);
};

Since it’s a dynamic field name I’m not really sure how to sample it properly, or even if I need to. If I don’t then I’m not sure why I’m receiving this error. If I do, then is there documentation on how to write this? I haven’t seen it in their documentation any where.

For some context, these are optional custom fields that they can fill in (but don’t) when making a customer. So sometimes it’ll load blank.

sample: {
      id: 123,
      first_name: "Debbie",
      last_name: "Cardone",
      display_name: "Mrs Debbie Cardone ()",
      created_at: "2018-12-03T18:42:15-06:00",
      company_name: "CReason",
      title: "Mrs",
      notes: "Test Notes",
      balance: "0.0",
      revenue: "0.0",
      is_lead: true,
      is_imported: false,
      marketing_source: "Zapier",
      is_recurring: false,
      is_churned: false,
      is_new: true,
      preferred_payment_method: "Credit Card",
      birth_date: "2018-01-01",
      recurrence_frequency: "weekly",
      emails: [
        {
          address: "email@test.com",
          email_type: "Work",
          is_automatable: true,
        },
      ],
      phone_numbers: [
        {
          display_line: "(541) 555-3003",
          phone_number: "+15415553003",
          phone_number_type: "Mobile",
        },
      ],
      service_addresses: [
        {
          line1: "123 Line 1",
          line2: "Line 2",
          city: "Dallas",
          state: "TX",
          postal_code: "123 456",
          iso_country_code_2: "US",
          latitude: 12.0,
          longitude: 34.0,
          display_line: "123 Line 1 - Line 2. 123 456 Dallas TX",
        },
      ],
      billing_addresses: [
        {
          line1: "456 Line 1",
          line2: "Line 2",
          city: "Dallas",
          state: "TX",
          postal_code: "789 456",
          iso_country_code_2: "US",
          latitude: 12.0,
          longitude: 34.0,
          display_line: "456 Line 1 - Line 2. 123 456 Dallas TX",
        },
      ],
      custom_fields: [
        {
          label: "Alarm code",
          value: "1234#",
        },
      ],
    },

Thanks in advance, sorry if this is blatantly obvious!