Why am I able to authenticate against REST API version2 and not against version3

[Adam Gyõri]

Good evening team, we have been using JIRA REST API version 2 for quite some time, specifically the request to fetch the USER:

https://globalwebindex.atlassian.net/rest/api/2/user/search?query="

We are trying to switch to version 3 using:
"https://globalwebindex.atlassian.net/rest/api/3/groupuserpicker?query="

For version 3 we are getting following response:
403 Forbidden
You are not authenticated. Authentication required to perform this operation.

We are using generated tokens via https://id.atlassian.com/manage-profile/security/api-tokens , then encoding the "email:token" string with BASE64. And creating request like:

curl -D- \

-X GET \

-H "Authorization: Basic encodedMailAndToken" \

-H "Content-Type: application/json" \

"https://globalwebindex.atlassian.net/rest/api/3/groupuserpicker?query=agyori@gwi.com&maxResults=50"

with response: You are not authenticated. Authentication required to perform this operation.

The thing I can not comprehend is why are we able to authenticate against version 2 and not against version 3. 

If you have any suggestion it would massively help us, thank you in advance.

[Mikael Sandberg]

You may want to to check the headers you are sending, based on the documentation the groupuserpicker is expecting Accept: application/json, not Content-Type.

[Adam Gyõri]

Great point, thank you Mikael ! But still "403 You are not authenticated. Authentication required to perform this operation."
Does anything else occur to you ?

[Mikael Sandberg]

No nothing else looks odd, I just know that some endpoints are particular when it comes to the headers, for example there are Confluence endpoints that expect Content-Type instead of content-type even though headers should not be case sensitive.

[Adam Gyõri]

Ok thank you though.

[Adam Gyõri]

Update the permission Issue seems to only be related to any request related to users.
I am without any issue able to fetch projects or a single project using: /rest/api/3/project

Could it be the case that I should probably ask somewhere for some additional permissions?