#39959 catalog_product_save_before observer throws date-related error when using REST API without store-level values (getFinalPrice() issue)

Updated special price logic to ensure date formats are handled consistently when calculating and setting the "special from" date. This improves compatibility and prevents potential type issues with date-related operations.

Author: KrasnoshchokBohdan

app/code/Magento/Catalog/Model/Product/Type/Price.php

@@ -451,16 +451,10 @@ protected function _getCustomerGroupId($product)
      */
     protected function _applySpecialPrice($product, $finalPrice)
     {
-
-        $specialPriceFrom = $product->getSpecialFromDate();
-        if ($specialPriceFrom instanceof \DateTimeInterface) {
-            $specialPriceFrom = $specialPriceFrom->format('Y-m-d H:i:s');
-        }
-
         return $this->calculateSpecialPrice(
             $finalPrice,
             $product->getSpecialPrice(),
-            $specialPriceFrom,
+            $product->getSpecialFromDate(),
             $product->getSpecialToDate(),
             WebsiteInterface::ADMIN_CODE
         );

app/code/Magento/Catalog/Observer/SetSpecialPriceStartDate.php

@@ -39,7 +39,8 @@ public function execute(\Magento\Framework\Event\Observer $observer)
         /** @var  $product \Magento\Catalog\Model\Product */
         $product = $observer->getEvent()->getProduct();
         if ($product->getSpecialPrice() && $product->getSpecialFromDate() === null) {
-            $product->setData('special_from_date', $this->localeDate->date()->setTime(0, 0));
+            $product->setData('special_from_date',
+                $this->localeDate->date()->setTime(0, 0)->format('Y-m-d H:i:s'));
         }
         return $this;
     }