Submit workflow to approval after calling SubmitStage function

Lets say I have 5 stage workflow. When workflow comes to stage 4 (from any stage), stage says: "Waiting for Submit". Then, user needs to click "Submit" button to send that stage to approval, and then stage says: "Waiting for approval". I need to do this automatically from code.

I'm using PSI function SubmitStage to go to another stage of a workflow (for example from stage 2 to stage 4):

Guid tResult = tWf.SubmitStage(projectUID, tEptUID, true, tStageGuid);

And workflow skips to stage 4, but not straight  to approval. User still needs to click "Submit" button manually to send that stage to approval.

I've tried to use the same function twice, but it still submits only once. How can I submit that stage directly to approval?