"Thank you! Goodbye!"
If any of you would like to look up the full meanings and uses of individual characters, I can definitely recommend the Han Trainer Dictionary online https://dictionary.hantrainerpro.com/chinese-english/. It's a wonderful resource!
From the information there: 谢 = to thank, to wither, to apologize, to excuse oneself, to thank somebody for something 谢谢 = thank you, thanks, vote of thanks 你 = you, 2nd person singular 再 = again, once more, anew, any more, any longer 见 = to see, to meet, to refer to, opinion, insight, to interview, view, sight, catch sight of, interview
The dictionary also lists additional information on the characters and words, such as audio pronunciation, common words in which the characters are used, words with similar meaning, other characters with the same pronunciation, etc.
Xie xie The second ‘xie’ is said slightly softer than the first one. There are many different meanings and cultural references wrapped up in these two words. The character ‘xie’ is a combination of ‘to speak’ and ‘to shoot’. In literature, it can be used to excuse one self or to make an apology. Xie is also a common surname in China, 0.8% of the population has the surname Xie. While 0.8% may not seem like a huge proportion of people, when it is applied to the 1.3 billion people of China, we are left with a number bigger than the population of many other countries. Pronunciation Xie xie is said in the fourth tone, so your voice must go down when you say it. To get the pronunciation right, the shape of your mouth is important. Smile widely and show both your upper and lower sets of teeth. When pronouncing the second ‘xie’, say it in a softer voice.
I've just tried using Western punctuation with and without spaces, and that does seems to be the case. With spaces it's rejected, and without, it's not. I guess it's just the spaces. I was basing my observation on other students' rejected answers as posted in their comments, showing Western punctuation both with and without spaces. Looks like those without could have been transcription errors.
That said, Western punctuation doesn't have the appropriate built-in spacing, so it doesn't make sense to use it for writing in Chinese in any event, and those who use it do tend to use spaces too, to compensate, which my test just now shows will be marked wrong.
(I knew we could get away with leaving out the punctuation altogether, though in its original state, the Chinese course required punctuation in the Chinese sentences.)