How to complete a web form task of external forms?

Can I use CompleteWorkItem to complete it as following in web form?

http://xxx:13490/AgilePointServer/Workflow/CompleteWorkItem/B81F005056990C1A11CC939000C341FC

I got the folloing return but the task is not completed.Pls help,tks!

{"ActivityInstID":"B81F005056990C1A11CC938FE29D5414","AutoStart":true,"Diagnostic":true,"EndDate":"\/Date(-62135596800000)\/","Entries":1,"Error":null,"EventID":"B81F005056990C1A11CC93A78A800FAA","EventName":"CompleteWorkItem","HighPriority":true,"ParamsXml":"<?xml version=\"1.0\" encoding=\"utf-8\"?><WFEvent><param name=\"ProcInstID\" value=\"B81F005056990C1A11CC938FE29D5407\" \/><param name=\"ActivityInstID\" value=\"B81F005056990C1A11CC938FE29D5414\" \/><param name=\"ClientData\" value=\"\" \/><param name=\"HighPriority\" value=\"True\" \/><param name=\"WorkItemID\" value=\"B81F005056990C1A11CC939000C341FC\" \/><\/WFEvent>","ParentProcInstID":"","ProcDefID":"","ProcInstID":"B81F005056990C1A11CC938FE29D5407","ProcInstName":"","Sender":"xxx\\000xxxxx","SentDate":"\/Date(1645510834676+0800)\/","SourceWorkItemID":""

,"Status":"Sent","TenantID":null,"UserID":"","WorkItemID":"B81F005056990C1A11CC939000C341FC","WorkObjectID":"","WorkObjectInfo":""}