Answer:
What I will write is "I'm sorry, and this may be the last letter I can send you because I can't send for some reason."
other answer:
I don't have anything to write because I know I can't send a letter to the person I want to send it to.
Explanation of other answers:
You don't have to write because if you can't send a letter, the letter you want to send will be useless if you can't send it to the person you want to send.
Ps: Please translate it to Tagalog since I'm not allowed to use Tagalog to answer your question
