The decoder has a "header" of a few bytes and then "0a". Currently the header is "31 31 38 37 0a". If you have more (e.g. 55 aa in front) or less than that (e.g. some of the 31 missing), try adding it manually. If the header is completely different, congratulations! You probably have a new message!
The complete message has start and end markers consisting of "aa 55" repeated. Trim these.
For a surprise, try clicking somewhere in the field above. I'm sorry selection doesn't work right now.
These XOR'ed symbols (in order of appearance) could not be decoded: