I am using this library to decrypt a CFB cipher 40 characters long, with a segment size of 16. It fails from this error:

if ((plaintext.length % this.segmentSize) != 0) {
throw new Error('invalid plaintext size (must be segmentSize bytes)');
}

However, when removing these line I am able to successfully decode the string.

Is this error incorrect? I was thinking segmentSize would be in bits and not bytes, so 40 bytes should be divisible into 16 bits without issue.