Hill Cipher how to encrypt and decrypt when both “I” and “J” are in plaintext

In Hill Cipher, let's assume the key is "KEYWORD" and I want to encrypt "JUICE", so after encryption, I get "GXLBWU", and when decrypt ciphertext I get back "IUICEX" not "JUICE". So my questions are:

1. So how do a receiver know where to put "J" after decryption?
2. Does he just have to guess it?
• Firstly, remove X that has a very low frequency in English. Next, guess. – kelalaka Jul 8 '19 at 12:01

In the Hill cipher, the key is a 2x2 matrix over some $$\mathbb{Z}_n$$, often with $$n=26$$, which is inconveniently non-prime, not a word. No I and J merging are needed there; we can choose any $$n \ge 26$$ and add extra characters (like spaces) for convenience.