The structure of the certificate array ($certificate)

/**
 * Certificate data
 *
 * array['id'] int certificate ID
 * array['code'] string certificate code
 * array['to'] string Field "To"
 * array['from'] string Field "From"
 * array['send'] string Field "Method of sending the certificate". Available values: email, post, user, not
 * array['message'] string Field "Message"
 * array['amount'] float Field "Amount"
 * array['currency'] string Field with currency
 * array['state_id'] int Certificate state ID
 * array['email'] string Field "Email" for parameter send = email
 * array['post'] array Shipping address for parameter send = post
 * array['post']['country'] string Country iso3letter format
 * array['post']['region'] int Region ID
 * array['post']['city'] int City name
 * array['post']['street'] int Street field
 * array['post']['postcode'] int Postcode
 * array['post']['phone'] string Phone
 * array['create_contact_id'] int Contact ID, who created the certificate
 * array['create_datetime'] string Create datitime
 * array['order_id'] int Order ID, where the certificate was created
 * array['contact_id'] int Contact ID that the certificate is intended for. Required, if parameter send = user
 * array['use_limitations'] int Use the limitations or not. Available values: 1 or 0
 * array['limitations'] array Limitations data
 * array['limitations']['expired'] string Expired date of the certificate in format: Y-m-d
 * array['limitations']['lifetime'] int Lifetime of the certificate in days.
 * array['limitations']['max'] float The maximum amount that can be spent in %. Specify values from 0 to 100
 * array['limitations']['min'] array Information about the minimum order amount
 * array['limitations']['min']['value'] float Minimal order sum
 * array['limitations']['min']['currency'] string Currency of the minimal order sum
 * array['lifetime_left'] int The remaining number of days before the certificate expires. Appears if limitations are used
 * array['lifetime_expired'] string Date of expiry of the certificate. Appears if limitations are used
 * array['is_expired'] int Appears only if the certificate has expired
 * array['usage'] array Data about the usage of the certificate
 * array['usage']['type'] string Certificate type: disposable or multiple
 * array['template'] string Certificate template
 * array['template_is_changed'] int Has the standard template been changed
 * array['default_template'] string Symbolic code of the default template.
 * array['products'] array Free products
 * array['products'][]['id'] int product or sku ID. Depends on parameter "type" (see below)
 * array['products'][]['certificate_id'] int certificate ID
 * array['products'][]['product_id'] int product ID
 * array['products'][]['sku_id'] int sku ID
 * array['products'][]['name'] string Product name
 * array['products'][]['price'] float Price of the product at the time of ordering the certificate
 * array['products'][]['type'] string Product type: common product or definite sku. Available values: products or skus
 *
 * @param array $certificate (See the parameters above)
 * @return array
 **/
$certificate = [
    'id' => 51,
    'code' => 'GC-TTWQ9CKX96EJE',
    'to' => 'Best customer', 
    'from' => 'Favourite store', 
    'send' => 'email',
    'message' => '', 
    'amount' => '50', 
    'currency' => 'USD', 
    'state_id' => 5,
    'email' => 'test@test.com',
    'post' => [
        'country' => 'rus',
        'region' => '77',
        'city' => 'Moscow',
        'street' => 'street, building, apt',
        'postcode' => '353535',
        'phone' => '89999999999',
        'address' => '353535, Russian Federation, Moscow, street, building, apt'
    ],
    'create_contact_id' => 5,
    'create_datetime' => '2020-08-17 08:08:30',
    'order_id' => 399,
    'contact_id' => 7, 
    'limitations' => [
        'expired' => '2040-10-28',
        'lifetime' => 30,
        'max' => 100,
        'min' => [
            'value' => 10,    
            'currency' => 'USD'
        ]
    ],
    'usage' => [
        'type' => 'disposable'
    ],
    'lifetime_left' => 27,
    'lifetime_expired' => '2020-12-09',
    'is_expired' => 1,
    'template' => 'certificate HTML',
    'template_is_changed' => 1,
    'default_template' => 'template3',
    'products' => [
        [
            'id' => 8740,
            'certificate_id' => 51,
            'product_id' => 8740,
            'sku_id' => 36698,
            'name' => 'Product name',
            'price' => 1236.25,
            'type' => 'products',
        ],
        [
            'id' => 37898,
            'certificate_id' => 51,
            'product_id' => 8756,
            'sku_id' => 37898,
            'name' => 'Product name (sku)',
            'price' => 700,
            'type' => 'skus',
        ]
    ]