I believe writeuser is the system user and you are making post request that's why you are getting 405 in browser.
Go to configurations in felix http://servername:port/system/console/configMgr
Search for "user mapper service " or writeuser
you will see an entry like mentioned below
![DEBAL_DAS_0-1648537527097.png DEBAL_DAS_0-1648537527097.png](https://experienceleaguecommunities.adobe.com/t5/image/serverpage/image-id/39638i1F0DBD84DE571980/image-size/medium/is-moderation-mode/true?v=v2&px=400)
if it is not there then add one.
Please search for writeuser in http://aemhost:port/security/users.html like mentioned below -
![DEBAL_DAS_1-1648537662076.png DEBAL_DAS_1-1648537662076.png](https://experienceleaguecommunities.adobe.com/t5/image/serverpage/image-id/39639iD79562A2E2C8B913/image-size/medium/is-moderation-mode/true?v=v2&px=400)
if it is not there then create system user named: writeuser and add requisite permission to writeuser .
Hope this will help.