SFMC: How to update rows only when the specified key exists for data extension?

Question

There are a bunch of customer records that need to be updated for data extension.

there is and REST API: https://developer.salesforce.com/docs/marketing/marketing-cloud/guide/postDataExtensionRowsetByKey.html

but this API is working as follows:

Use this API to upsert multiple data extension rows. An upsert operation updates rows when the specified key already exists and inserts new rows when the specified key doesn't exist.

I need to update rows only when the primary key exists in the data extension and skip others without creating new records.

of course, I can make additional requests before the upsert operation to check which records don't exist and exclude them from the list but these are additional requests.

I'm wondering if there is a way to update records and avoid inserting new ones.

UPDATE: I found a solution by using the SOAP API instead of REST.

POST: https://<...>.soap.marketingcloudapis.com/Service.asmx

<?xml version="1.0" encoding="UTF-8"?>
<s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope" xmlns:a="http://schemas.xmlsoap.org/ws/2004/08/addressing" xmlns:u="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd">
    <s:Header>
        <a:Action s:mustUnderstand="1">UpdateOnly</a:Action>
        <a:To s:mustUnderstand="1">https://<...>.soap.marketingcloudapis.com/Service.asmx</a:To>
        <fueloauth xmlns="http://exacttarget.com">{{token}}</fueloauth>
    </s:Header>
    <s:Body xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
       <UpdateRequest xmlns="http://exacttarget.com/wsdl/partnerAPI">
        <Options>
            <SaveOptions>
                <SaveOption>
                    <PropertyName>DataExtensionObject</PropertyName>
                    <SaveAction>UpdateOnly</SaveAction>
                </SaveOption>
            </SaveOptions>
        </Options>
        <Objects xsi:type="DataExtensionObject">
            <CustomerKey>CustomerKeyID</CustomerKey>
            <Keys>
                <Key>
                    <Name>Email</Name>
                    <Value>[email protected]</Value>
                </Key>
            </Keys> 
            <Properties>
                <Property>
                  <Name>Email</Name>
                  <Value>[email protected]</Value>
               </Property>
               <Property>
                  <Name>FirstName</Name>
                  <Value>John</Value>
               </Property>
               <Property>
                  <Name>LastName</Name>
                  <Value>Smith</Value>
               </Property>
            </Properties>
         </Objects>
         <Objects xsi:type="DataExtensionObject">
            <CustomerKey>CustomerKeyID</CustomerKey>
            <Keys>
                <Key>
                    <Name>Email</Name>
                    <Value>[email protected]</Value>
                </Key>
            </Keys> 
            <Properties>
                <Property>
                  <Name>Email</Name>
                  <Value>[email protected]</Value>
               </Property>
               <Property>
                  <Name>FirstName</Name>
                  <Value>Jane</Value>
               </Property>
               <Property>
                  <Name>LastName</Name>
                  <Value>Doe</Value>
               </Property>
            </Properties>
         </Objects>
      </UpdateRequest>
    </s:Body>
</s:Envelope>