Posit Workbench RStudio session remains in pending mode

Dear community, I am a newbie at running AWS services. I am trying to run RStudio on SageMaker. After several sessions with AWS technicians I finally managed to get the Posit Workbench license running on SageMaker. I created a domain and a user with all permissions and the RStudio option does indeed appear for my user. When I click on it the Posit Workbench opens, I am trying to create a new session, but then nothing happens. All sessions I tried to create, remain in pending mode. What am I missing? What can I do to remedy this situation?