why is Graph API Update not working but other functions working

Hello i am getting an error when using Microsoft graph api, i am getting a 403 error when I am updating a planner task.

{StatusCode: 403, ReasonPhrase: 'Forbidden', Version: 1.1, Content: System.Net.Http.StreamContent, Headers: { Transfer-Encoding: chunked request-id: 7c6e6c64-60e8-4d65-a248-c91841f8f8ca client-request-id: 7c6e6c64-60e8-4d65-a248-c91841f8f8ca x-ms-ags-diagnostic: {"ServerInfo":{"DataCenter":"North Europe","Slice":"SliceC","Ring":"3","ScaleUnit":"001","Host":"AGSFE_IN_70","ADSiteName":"NEU"}} Duration: 184.823 Strict-Transport-Security: max-age=31536000 Cache-Control: private Date: Wed, 03 Oct 2018 06:24:41 GMT Content-Type: application/json }}

I have also created my own plan to create out my tasks and assign them accordingly

This issue only occurs on the update, other functions like the read, create and delete work without any issue.

Any help would be appreciated to solve this issue