"Yo no puedo comer pescado."
Translation:I cannot eat fish.
I am not allowed would imply you do not have permission. I cannot eat fish does not imply a reason. It may be due to allergy or causing an upset stomach.
Yes, I understand the difference between to be allowed and to can, but this is just another matter of context which is not provided. And without context we can't tell for sure which of the latter is correct.
Sorry about the confusion. My answer was vague. "Yo no puedo comer pescado" would most closely mean "I cannot eat fish". Both the spanish and english statement can be used to mean "I am not allowed to eat fish". I am not sure how Duolingo decides what constitutes a right or wrong answer. Either way, that statement could be used as you describe.
Before" cannot you sleep"wrong,now "I cannot eat fish"right .WhY?Please,explain it to me,I am confused.
If your first sentence you placed the negative before the subject instead of the verb. The negative applies to the verb. It would be either "Can you not sleep?" or You cannot sleep?
That would be similar to saying "¿No tú duermes?"