Hi !

The qualifying criteria for AIIMS PG is 50 percentile for all the categories whether reserved or unreserved , and you have percentile less than 50 , it means that you did not qualify the exam. The offer letter you got is also saying that you have not been alloted any seat , it is to inform you about the status of your allotment , since you have not qualified the exam , you are not eligible to get a seat in any round.

Hope it helps !

Check out the following link for more information:

https://medicine.careers360.com/articles/aiims-pg-cut-off