projects api call work on zoho creator but doesn't work when called from other zoho app

projects api call work on zoho creator but doesn't work when called from other zoho app

Greetings

i have the habit of creating and testing custom functions on zoho creator before moving them to the apps where i want to use them in automated workflows.

i've been testing the zoho projects api call "get users" to get a list of all projects users. this is not included in the default projects connection.

  1. usersList = invokeurl
  2. [
  3. url :"https://projectsapi.zoho.com/restapi/portal/"portal"/users/"
  4. type :GET
  5. connection:"test_projects_connection"
  6. ];
i've tried this invokation from an admin and a user account on creator and it worked fine on both.
then i moved my custom function to zoho books where i'm going to use it, i just had to change the connection. the invocation worked only on the admin account. while on the employee account it returned ""code":6401,"message":"Unauthorized Access"}". although it worked fine on the employees creator side. why am i getting this? how can i fix it?