For what it's worth, I didn't downvote your question What does “Yes, you can. But you may not.” mean? I didn't downvote it because you told us what the context was; I didn't upvote it because you showed no research effort. To me, this is not really a good question. The reason is that it does not tell us how you have tried to solve this problem on your own before asking the question in ELL. ELL (and SE in general) is a bit different from Yahoo! Answers, Reddit, WordReference, Quora, etc. Here, we really want the members of our community to show some "research effort".
I think this EL&U post Difference between “can” and “may”: Can/May I have your pen please? would have been a perfect source/reference to cite as your "research effort". You should then have explained why the answers in this EL&U post were not sufficient to address your problem. I, however, feel the answers here fully answer your question. But even if you didn't like them for some reason, you should have linked this question.
Merriam-Webster has a nice post on this: Can you use 'can' or must you use 'may'?
A student raises their hand and asks the teacher “Can I go to the bathroom?” and the teacher responds, “I don’t know—can you?”
You will get many results if you simply google "you can but you may not". I haven't even tried other variations of this. And it is already clear to me from the above sources that the answer is right there. This is research which you should have done.
Search Results from ELL:
- “May I have a glass of water” vs. “Can I have a glass of water”: which is better, “may I” or “can I”, when asking for something?
- The tendency to replace may I with can I
The upvotes you got on your question is due to a number of reasons, as stated by Glorfindel.
I am wondering if you actually looked at our help center rules and meta questions regarding what constitutes a good question.
From How do I ask a good question?
Search, and research
Have you thoroughly searched for an answer before asking your question? Sharing your research helps everyone. Tell us what you found and why it didn’t meet your needs. This demonstrates that you’ve taken the time to try to help yourself, it saves us from reiterating obvious answers, and above all, it helps you get a more specific and relevant answer!
Some of us have given you some suggestions on how you can improve your questions. I have personally left comments on some of your questions asking you to add details or "research effort", but you haven't done so in any of your questions. I, myself, edited one of your questions to include your "thought process" (which qualifies as "research effort") that you had mentioned in response to my comment. But you didn't improve any of the following questions.
Here are some instances where we have tried to tell you this.