@cris_555 , thank you for your answers.
Once you leave the country in 2024, your F-1 would terminate ( you also have to tell the Immigration that you are leaving). The visa is valid generally only while you are domiciled here in the US ( except for short stays abroad for vaca etc. )
So for 2025 , your counting of days present starts when you are admitted with the H1-B visa.
Bolivia does not have a tax treaty with the US. There is also NO totalization Agreement in place. Therefore you have to contribute to FICA while on H1-B .
Is there more I can do for you ?
