<route url="/V1/attribute/AttributeOption" method="POST">
    <service class="VendorModuleApiAttributeInterface" method="AttributeOption"/>
</route>

<?php
namespace VendorModuleApi;

interface AttributeInterface
{
 /**
 * POST for attribute api
 * @param mixed $param
 * @return array
 */

  public function AttributeOption($params);
}

<?php
   namespace VendorModuleModel;
   use VendorModuleApiAttributeInterface;
   use MagentoEavSetupEavSetupFactory;
   use MagentoStoreModelStoreManagerInterface;
   class Attribute implements AttributeInterface
  {
   protected $_eavSetupFactory;
   protected $_storeManager;
   protected $_attributeFactory;
   protected $eavAttributeFactory;
   protected $attributeOptionManagement;
   protected $productFactory;
   private $productAttributeRepository;
   protected $objectManager;
   public function __construct(
    MagentoFrameworkObjectManagerInterface $objectManager,
    MagentoEavSetupEavSetupFactory $eavSetupFactory,
    MagentoStoreModelStoreManagerInterface $storeManager,
    MagentoCatalogModelResourceModelEavAttribute $attributeFactory,
    MagentoEavModelEntityAttributeFactory $eavAttributeFactory,
    MagentoEavApiAttributeOptionManagementInterface $attributeOptionManagement,
    MagentoCatalogModelProductFactory $productFactory,
    MagentoCatalogModelProductAttributeRepository $productAttributeRepository
) {
    $this->_objectManager = $objectManager;
    $this->_eavSetupFactory = $eavSetupFactory;
    $this->_storeManager = $storeManager;
    $this->_attributeFactory = $attributeFactory;
    $this->eavAttributeFactory = $eavAttributeFactory;
    $this->attributeOptionManagement = $attributeOptionManagement;
    $this->productFactory = $productFactory;
    $this->productAttributeRepository = $productAttributeRepository;
  }

  public function AttributeOption($params) {
      // looking for logic to create / update options from request
  }

}

{
"params":{
    "Type": "create",
    "attribute_id" : "159",
        "OptionValues": [
         {
            "OptionId": "01",
            "OptionName": "Test"
         },
         {
            "OptionId": "Null",
            "OptionName" : "Test2"
         }
     ]
   }
}

$OptionValues = json_decode('{"params":{"Type": "create", "attribute_id" : "159", "OptionValues": [{ "OptionId": "01", "OptionName": "Test"}, { "OptionId": "Null", "OptionName" : "Test2"}]}}');

foreach($OptionValues->params->OptionValues as $optValue){
    $optionVal = $option->OptionName;
    if($option->OptionId == NULL){
        //Create Code
    }
    else{
        //Update Code
    }
}