begriffs/postgrest

Hi all, I have a strange bug with this simple "logout" RPC function

create or replace function logout() returns void as $$
begin
  perform set_config('response.headers', '[{"Set-Cookie": "jwt=0; Path=/;expires=Thu, 01 Jan 1970 00:00:01 GMT; HttpOnly"}, ...blablabla...]', true);
end;
$$ language plpgsql IMMUTABLE; -- IMMUTABLE can be GET
GRANT EXECUTE ON FUNCTION logout TO "anon", "user", "admin";

But the set_config only occur "sometimes", as you can see with the same curl command I get different headers response.

$ curl -v 'http://0.0.0.0/api/rpc/logout'
*   Trying 0.0.0.0:80...
* Connected to 0.0.0.0 (127.0.0.1) port 80 (#0)
> GET /api/rpc/logout HTTP/1.1
> Host: 0.0.0.0
> User-Agent: curl/7.84.0
> Accept: */*
> 
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Server: nginx/1.21.6
< Date: Tue, 02 Aug 2022 00:07:56 GMT
< Content-Type: application/json; charset=utf-8
< Transfer-Encoding: chunked
< Connection: keep-alive
< Content-Range: 0-0/*
< Set-Cookie: jwt=0; Path=/;expires=Thu, 01 Jan 1970 00:00:01 GMT; HttpOnly
< Set-Cookie: id=0; Path=/;expires=Thu, 01 Jan 1970 00:00:01 GMT;
< Set-Cookie: role=0; Path=/;expires=Thu, 01 Jan 1970 00:00:01 GMT;
< 
* Connection #0 to host 0.0.0.0 left intact
""

and just 2 second later, no more Set-Cookie ...

$ curl -v 'http://0.0.0.0/api/rpc/logout'
*   Trying 0.0.0.0:80...
* Connected to 0.0.0.0 (127.0.0.1) port 80 (#0)
> GET /api/rpc/logout HTTP/1.1
> Host: 0.0.0.0
> User-Agent: curl/7.84.0
> Accept: */*
> 
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Server: nginx/1.21.6
< Date: Tue, 02 Aug 2022 00:07:58 GMT
< Content-Type: application/json; charset=utf-8
< Transfer-Encoding: chunked
< Connection: keep-alive
< Content-Range: 0-0/*
< 
* Connection #0 to host 0.0.0.0 left intact

It feels like some kind of "caching" issue but I don't see how/why/what I did wrong