how to know the decryption is not the real message

[Taifour-Taoutaou]

Hi, I'm studing PQC schem : Light Kyber (Baby Kyber).
When I am trying to do some examples of KeyGen(), Enc(), and Dec(), sometimes the decryption gives me the same message I sent but sometimes it doesn't.

As an example my message is m=5 but after decryption it's m'=8, so if I'm just a receiver how to know that "8" is not the correct message, or if I'm the sender how to know that it would give an error so I will change "r" or "e1", ...

I know the failure depends on matrixes s, e, e1, e2, r, but I don't know how to detect the error before sending the message.
Thank you

[cryptojedi]

What exactly is the definition of Baby Kyber? Are you using code from this repository?