"There is a booth ahead."
It would be understood as 'The booth is ahead'.
Russian puts new information towards the end of the sentence. So, in «Кио́ск впереди́», «киоск» is something knows (hence the article 'the'), and the fact that it's «впереди́» is the new information we tell in the sentence.
In «Впереди́ кио́ск», you tell something new about what's ahead, and the fact that «кио́ск» is what's ahead is the new information.
Please note that this is not a 100% rule because you can also mark the new information with intonation, and the intonation can 'override' the word order. However, we don't usually mark intonation in writing, so we usually avoid the word order that requires non-neutral intonation in writing.
I think it sound OK and could be used as a translation of "There is a booth ahead". I don't know if Duolingo accepts it, but if it doesn't, I think it can be reported.
On another question "Is there a theatre here?" есть is mandatory. Why is it supposed to be left out here? Is it because the existence of several kiosks somewhere in the area is already assumed? Would '"Впереди есть киоск." be suitable if we were in a place where we wouldn't usually expect to find any kiosks?
In «Впереди́ е́сть кио́ск?», «е́сть» is actually emphasised by intonation. It constitutes the main piece of information asked: is there a kiosk, or isn't there one?
In «Впереди́ кио́ск» and «Впереди́ есть кио́ск», you'd still emphasise «кио́ск». «Кио́ск» is the main piece of information. The existence of something ahead of assumed, and the main piece of information is that this something ahead is «кио́ск».
The versions with emphasised «есть» (the default word order for this is «Впереди́ кио́ск е́сть»; «Впереди́ есть кио́ск» can be used this way too, if you emphasises «есть» with intonation) are likely to be used when refuting a previous claim about the absence of kiosks, or when asnwering a question «Впереди́ е́сть кио́ск?».
You're emphasizing the existence of the booth, as in "Look, there's a booth ahead! Maybe they have ice cream!"
Why wouldn't «есть» be acceptable here?
This could work only if the booth literally fell on its side (but I'm not sure if that even happens, I couldn't find such photos). Or if «кио́ск» is understood not as a kiosk itself but as a geographic area around some known kiosk. Both cases are pretty improbable.
«Стои́т» instead of «лежи́т» should be acceptable, though.