Transferring orders from external sites via PHP API script

Greetings. We are now accepting orders from landing sites according to the script. Example https://newtrend-shop.com.ua/ua/winter2022/ In each form, we have a script like this: <form id="order_form" class="order_form orderformcdn" action="send.php" method="post"> <input type="hidden" name="utm_source"> <input type="hidden" name="utm_medium"> <input type="hidden" name="utm_campaign"> <input type="hidden" name="utm_content"> <input type="hidden" name="utm_term"> <input type="hidden" name="price_1" value="1399"> <input type="hidden" name="product_id_1" value="382886"> <div class="input"> <input name="name" type="text" placeholder="Enter your name" required> </div> <div class="input"> <input name="phone" type="text" placeholder="Enter phone" data-inputmask="'mask': '+389999999999'" minlength="16" maxlength="16" required> </div> <div class="input"> <select required name="custom_sizeProdOrder"> <option value=""> Choose a rozmіr </option> <option value="48/50"> 48/50 </option> <option value="52/54"> 52/54 </option> <option value="56/58"> 56/58 </option> There is a product ID and filters for it. But when we select a filter for example 56/58 of the wrong size, but of a different ID, the filter 56/58 is pulled up, but the ID is basic How to write a script correctly so that the product ID is replaced by the filter? Thank you in advance for your response.