"You do not have to leave right away."
Translation:Du musst nicht sofort gehen.
Should "Sie müssen sofort nicht gehen" be acceptable?
No. Your sentence tells someone that they have to do something immediately, and the thing they have to do immediately is "not go".
That is, Sie müssen sofort + nicht gehen = "You must immediately" + "not go".
An extremely odd thing to say and certainly not the same meaning as the original sentence.
"Du musst gerade nicht gehen" would be used, if you wanted to imply that under the current circumstances the person does not have to leave (e.g. if there is a storm outside), but if the situation changes, this might change as well. "Du musst nicht sofort gehen" means "you don't have to leave right at this instance"
"Abfahren" is pretty much only used in the context of a train. That means, if a train is leaving you can use "abfahren", but only in this context. The word leave can be translated in many ways like "verlassen" (exit something), "gehen" or "weggehen" (literally to walk away by foot, but it is commonly used in a more general sense like "to go away").
She does not have to eat it: “Sie muss nicht es essen” – marked wrong, should be “Sie muss es nicht essen” You do not have to leave right away: “Du muss sofort nicht gehen” – marked wrong, should be “Du musst nicht sofort gehen” What are the rules for the placement of nicht, because I don’t understand the difference
If "nicht" negates the complete sentence, it comes at the end of the sentence, only followed by infinitives, participles and second parts of split verbs. That's the case in "Sie muss es nicht essen".
If only a specific part of the sentence is negated, "nicht" stands directly in front of this part. This is the case in the second example. The sentence does not say that you don't need to leave at all, it only says that this need not be the case immediately. So the "sofort" is negated, resulting in "Du musst nicht sofort gehen".
As a native speaker, I have to partially agree with you. But in this context, I have to say, that there is no way to negate the whole sentence by just reordering it. The only way to negate the whole meaning that comes to my mind would be to use something like "Du musst überhaupt nicht gehen" or to turn it around completely "Du kannst auch hier bleiben"
"Sie brauchen nicht zu gehen" -- which I learned in my first German course is the proper negation of Müssen -- is not accepted. This translation seems more like "You must not go right away." (as in, it would be deadly to leave at this time, but not if the person waits for a bit.)
I believe you need a 'zu': Du brauchst sofort nicht zu gehen.
When negating muessen with brauchen, you need a 'zu'
Ich muss gehen. --> Ich brauchen nicht zu gehen.
Ich muss spielen --> Ich brauche nicht zu spielen.
HOWEVER, I don't think Duolingo accepts that. They want 'musst nicht'
The thing about the "zu" is korrekt. "brauchen" needs it, in contrast to "müssen".
But you used several wrong forms and word orders. Your examples should be:
"Su brauchst nich sofort zu gehen"
"Ich brauche nicht zu gehen".
But it is used less frequently than "müssen".
When you want to negate the complete sentence, the usual pisition of "nicht" is at the end of the sentence, but before any infinitives, participles and second pafrts of split verbs.
So "Du musst (jetzt) nicht gehen" (You don't have to leave (now)") is the negation of "Du musst (jetzt) gehen" ("You have to leave (now)").
But in German you have another option that has a different meaning: putting the "nicht" in front of any part of the sentence (except for the verb) negates just this part.
So "Du musst nicht jetzt gehen" (in English also "You don't have to leave now"but maybe with more emhasis on the word "now") means something like: "you might have to leave, but not now". In your second example ("right away") this is certainly what was intended.
It is a grammatically correct sentence, but it has a slightly different meaning.
In "Du musst jetzt nicht weggehen" the "nicht" stands in the usual position to negate the complete sentence, so it is the opposite of "Du musst jetzt weggehen", thus meaning "It is not the case that you have to leave now".
In "Du musst nicht jetzt weggehen" the "nicht" only negates the "jetzt" ("now"). So it means "It may well be the case that you might have to leave, but definitely not now".
The rule where to put the "nicht" is definitely not "after the modal verb", that is only coincidence.
There are two different positions for the "nicht":
1.) if you negate the complete sentence (same as negating the verb), "nicht" goes to the "end of the mid-field", i.e. to the end of the sentence, potentially followed only by certain elements like infinitives, participles, second parts of separable verbs and predicative complements.
2.) If you want to negate only a specific element, then the "nicht" comes immediately before this element.
The second is the case here. You are not negating that you have to leave at all, but negate only the "right away". So the "nicht" comes dierectly before the "sofort".
In some exercises, "don't have to" is given as the mussen .... nicht form, and here it is mussen nicht ... . How do I tell where to put the nicht to negate the "must" or the modal verb? I've gotten so confused that I'm just guessing it in every exercise and getting it wrong. Can someone please explain what the two forms I mentioned above mean?
You should always quote the complete sentence, so we can see what might be the reason why it was not accepted.
If you speak of "fortgehen" as a replacement of "gehen": You could use this in principle, but it is not particularly common. It sounds a little declamatory or archaic.