For incoming calls on Roamer while abroad, your plan and operator need to allow call forwarding to a local Roamer number. Launch the app and enable/disable Incoming calls in settings following the instructions. You will be able to see if plan and operator allow call forwarding. Disable Incoming calls after you check so you are not using Roamer unintentionally.
Call forwarding did not work for you? No worries, there will be no incoming calls on Roamer abroad but nothing will stop you from making calls on Roamer regardless of your country, plan or network so please relax.