Why my configuration for SOLR uniqueKey with solr.UUIDField generates ERROR SolrException missing required field: id

Question

I want to use UUIDUpdateProcessorFactory to automatically generate UUID as the uniqueKey field for all new documents that will be created. I followed the given instructions & also tried already given solutions here & here but nothing worked. I am using solr version 9.1.1 on Ubuntu 22.04.1 LTS.
I amgetting the error: missing required field: id.
Following is my current configuration which is generating error:

solr-spec: 9.1.1
lucene-spec: 9.3.0

managed-schema.xml
-----------------------
<fieldType name="uuid" class="solr.UUIDField" indexed="true"/>
<field name="id" type="uuid" indexed="true" stored="true" required="true" multiValued="false" />
<field name="_root_" type="uuid" indexed="true" stored="false" docValues="false" />
<uniqueKey>id</uniqueKey>


solrconfig.xml
---------------
<updateRequestProcessorChain name="uuid">
    <processor class="solr.UUIDUpdateProcessorFactory">
      <str name="fieldName">id</str>
    </processor>
    <processor class="solr.RunUpdateProcessorFactory" />
</updateRequestProcessorChain>

 <requestHandler name="/update" class="solr.UpdateRequestHandler">
       <lst name="defaults">
         <str name="update.chain">uuid</str>
       </lst>
</requestHandler>

Error Message:

RequestHandlerBase   org.apache.solr.common.SolrException: [doc=null] missing required field: id

Please advise what I am missing?