What is the meaning of the saying of Imam Ridha (PBUH) ((and I am one of its conditions))?

Answer

In the name of Allah, it is meant that believing in Allah and being monotheist couldn’t be accepted unless you follow Ahlulbait (PBUH) and the infallible imams (PBUH). Therefore, It is a condition for accepting the actions. Since Imam Ridha is one of the Imams (PBUH), so he is one of the conditions. Allah is the All Guide and He knows best.