Invalid API key or access token (unrecognized login or wrong password)

I followed the instruction from the workshop to install a custom app in my Shopify store. But I still got an invalid API key error. I am not sure what could go wrong here. Please help.

  1. I got the Admin API access token from the installed custom app

  2. I made a post request to https://{yourstorename}.myshopify.com/admin/api/{latest-api-version}/graphql.json with header values

3.Then I got the invalid api key error..