Currently, there is a limitation to get more than 1000 assignable user. 

Using startAt parameter to set page offset for Fine Users REST API only works for first 1000 users. It does not return users with index more than 1000.

Steps to Reproduce

1. Add more than 1000 active users (e.g 1100 users)
2. Run following curl command to use Find Users REST API to get list of users:

   curl --request GET \
     --url 'https://<siteName>.atlassian.net/rest/api/3/user/search?startAt=1000&maxResults=100&query' \
     --header 'Authorization: Basic <email:apitoken(base64encoded)>' \
     --header 'Accept: application/json'
   

curl --request GET \
  --url 'https://<siteName>.atlassian.net/rest/api/latest/user/assignable/search?project=<Project Name>&maxResults=1000&startAt=1000' \
  --header 'Authorization: Basic <email:apitoken(base64encoded)>' \
  --header 'Accept: application/json'

Expected Results

Assuming there are >=1100 users in the site, this call should return list of users from index 1000 to index 1100

Actual Results

It returns no result

Notes

This works for users with index less than 1000, for example following curl command works fine:

curl --request GET \
  --url 'https://<siteName>.atlassian.net/rest/api/3/user/search?startAt=100&maxResults=100&query' \
  --header 'Authorization: Basic <email:apitoken(base64encoded)>' \
  --header 'Accept: application/json'