Getting below error message while rebuilding the index

SourceContex - Sitecore.Xdb.Collection.Indexing.Rebuild.IIndexRebuildFlow

System.Net.Http.HttpRequestException: at System.Net.Http.HttpResponseMessage.EnsureSuccessStatusCode (System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a) at Sitecore.Xdb.Collection.Search.Solr.SolrClient+d__6.MoveNext (Sitecore.Xdb.Collection.Search.Solr, Version=3.1.0.0, Culture=neutral, PublicKeyToken=null) at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089) at Sitecore.Xdb.Collection.Search.Solr.TaskRetryHelper+<>c+<b__1_0>d.MoveNex at Sitecore.Xdb.Collection.Search.Solr.IndexRebuildHelper+d__11.MoveNext (Sitecore.Xdb.Collection.Search.Solr, Version=3.1.0.0, Culture=neutral, PublicKeyToken=null) at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089) System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089) at Sitecore.Xdb.Collection.Search.Solr.IndexRebuildHelper+d__8.MoveNext (Sitecore.Xdb.Collection.Search.Solr, Version=3.1.0.0, Culture=neutral, PublicKeyToken=null) at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089) at Sitecore.Xdb.Collection.Indexing.Rebuild.IndexRebuildFlow+d__25.MoveNext (Sitecore.Xdb.Collection, Version=3.1.0.0, Culture=neutral, PublicKeyToken=null) at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089) at Sitecore.Xdb.Collection.Indexing.Rebuild.IndexRebuildFlow+RebuildStatusWatcher+<>c__DisplayClass5_0+<g__RunRebuildFlowCycle|0>d.MoveNext (Sitecore.Xdb.Collection, Version=3.1.0.0, Culture=neutral, PublicKeyToken=null) at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089) at Sitecore.Xdb.Collection.Indexing.Rebuild.TaskExtension+d__0.MoveNext (Sitecore.Xdb.Collection, Version=3.1.0.0, Culture=neutral, PublicKeyToken=null)