How to solve "missing fields" errors in Google Structured Data Types (schemas) - eg with product schema

how-to-solve-missing-fields-errors-in-google-structured-data-types-schemas.php

add_filter('seopress_schemas_auto_product_json', 'sp_schemas_auto_product_json');
function sp_schemas_auto_product_json($json) {
    // Returns schema as an array with 'property' => 'value'

    // Get the product offers
    $offers = $json['offers'];

    // Add sub-type MerchantReturnPolicy and deliveryTime to each offer
    if (!empty($offers)) {
        foreach ($offers as $key => $offer) {
            //hasMerchantReturnPolicy
            $offers[$key]['hasMerchantReturnPolicy'] =
                [
                    '@type' => 'MerchantReturnPolicy',
                    'applicableCountry' => 'FR',
                    'returnPolicyCategory' => 'https://schema.org/MerchantReturnFiniteReturnWindow',
                    'merchantReturnDays' => 120,
                    'returnMethod' => 'https://schema.org/ReturnByMail',
                    'returnFees' => 'https://schema.org/FreeReturn'
                ];

            // Check if 'shippingDetails' is present in the offer
            if (isset($offer['shippingDetails'])) {
                // Iterate through shipping details and add 'deliveryTime'
                foreach ($offer['shippingDetails'] as $k => $shippingDetail) {
                    $offers[$key]['shippingDetails'][$k]['deliveryTime'] =
                        [
                            '@type' => 'ShippingDeliveryTime',
                            'handlingTime' => [
                                '@type' => 'QuantitativeValue',
                                'minValue' => 0,
                                'maxValue' => 1,
                                'unitCode' => 'DAY'
                            ],
                            'transitTime' => [
                                '@type' => 'QuantitativeValue',
                                'minValue' => 1,
                                'maxValue' => 5,
                                'unitCode' => 'DAY'
                            ]
                        ];
                }
            }
        }
    }

    // Update the original JSON with modified offers
    $json['offers'] = $offers;

    return $json;
}