Is there any message on screen after return to login form?
At first login It makes full load data from web. It includes such reqests:
1. check plugin
<your web-server url>/index.php?c=api&m=active_plugin&plugin=vatapi
must return
{"plugin_state":1}
2. check credentials
<your web-server url>/index.php?c=api&m=login&username=<login>&password=<password>
must return:
{"token":"your token","username":"your login","user_id":,"company":"your company"}
3. load categories (using token from previouse step)
<your web-server url>/index.php?c=vatapi&m=list_members&srv=workspace&auth=<token>
must return a list of your workspaces
4. load tasks
<your web-server url>/index.php?c=vatapi&m=listing&srv=ProjectTasks&args={"status":"0"}&auth=<token>
must return a list of your active tasks
5. load timeslots
<your web-server url>/index.php?c=vatapi&m=listing&srv=Timeslots&auth=<token>
must return a list of your timeslots (may take some time on big database)
May you try this requests in browser? Does they work?