List all billing templates.

{  "results": [    {      "purchase": {        "currency": "str",        "products": [          {            "name": "string",            "quantity": 1,            "price": 0,            "discount": 0,            "tax_percent": 0,            "category": "string",            "total_price_override": null          }        ],        "total": null,        "language": "Default value is controlled in Company -> Brand section of merchant portal separately per each Brand used (default value, if no changes are made, is `en`). Brand to be used with corresponding Purchase/BillingTemplate specified using brand_id.",        "notes": "string",        "debt": 0,        "subtotal_override": null,        "total_tax_override": null,        "total_discount_override": null,        "total_override": null,        "request_client_details": [],        "timezone": "Europe/Oslo",        "due_strict": false,        "email_message": "string",        "metadata": {},        "single_attempt": false      },      "company_id": "b2e6a1c3-1a5e-44ae-a8fd-81f76fd715cf",      "number_of_billing_cycles": 0,      "is_test": true,      "user_id": "a169451c-8525-4352-b8ca-070dd449a1a5",      "brand_id": "1bb61461-e5e3-4ebb-8cc6-5b0c37f1b7da",      "title": "string",      "is_subscription": true,      "invoice_issued": "2020-04-30",      "invoice_due": 1619740800,      "invoice_skip_capture": false,      "invoice_send_receipt": false,      "subscription_period": 1,      "subscription_period_units": "months",      "subscription_due_period": 7,      "subscription_due_period_units": "days",      "subscription_charge_period_end": false,      "subscription_trial_periods": 0,      "subscription_active": false,      "subscription_has_active_clients": true,      "force_recurring": false,      "upsell_campaigns": [        "26b11f47-c6a7-4c09-b770-196490ac710e"      ],      "referral_campaign_id": "d2266e23-661a-4f4a-bd3d-2b530c5324d4",      "type": "string",      "id": "497f6eca-6276-4993-bfeb-53cbbbba6f08",      "created_on": 1619740800,      "updated_on": 1619740800    }  ],  "next": "string",  "previous": "string"}