Error while creating a post in LinkedIn page using LinkedIn API

I was stuck at this error:

{"Service Error Code": 100,"message": "Field Value validation failed in REQUEST_BODY: Data Processing Exception while processing fields [/author]","status": 403}

I used the post API: https://api.linkedin.com/v2/ugcPosts

and the body mentioned in the documentation accordingly: https://learn.microsoft.com/en-us/linkedin/marketing/community-management/shares/ugc-post-api?view=li-lms-unversioned&tabs=http

Should I need to allow the Access of Advertising API and Lead Sync API also? and then should I try or else is there any way to post it.

I used the organization ID from the URL when we click on the LinkedIn page.