"I always travel by myself."
It sounds like Japanese "ryo" to me. The standard Japanese r sound is a light, rolling R (tremulant) with only one vibration, and sometimes it sounds more like a D or an L. I practiced it aiming for something between those three. You might scare someone if you use a strong/long rolling r in Japan (if it's not in the local dialect).
Also, even though there seems to be as many sounds in both りょ and こう if you write it in romaji (ryo-kou both have 3 letters), the りょ should actually be as short as any single hiragana. It is divided into りょ-こ-う if you ask a Japanese person about the spelling. These sounds りゃ, りゅ, りょ are very foreign to my native language, so I actually practiced them a lot.
So i looked up "kazuto" at jisho.org.
Apparently, this spelling of "Kazuto" is a surname.
My guess would be that the reading robot that Duo uses is recognizing standalone "一人" as a surname, not "one person" or "alone".
( This misreading is still one of the most irritating things on duo for me ._. )
りょこう is a noun, "travel, trip".
~ます is a verb ending used simply to add more politeness and formality to the sound of the verb it attaches to.
します is the ~ます form of the verb する, "do".
- する "do" (regular plain form)
- します "do" (polite form)
You can't stick the verb ending ~ます onto a noun instead of a verb. ^^
する is an irregular verb, which is why this verb happens to change so drastically from する to し when attaching the ~ます verb ending. Regular verbs change too, but not such a major change:
- のむ (nomu) "drink" regular plain verb form
- のみます (nomi + ~masu) "drink" polite verb form.
I'm not sure, but I have a feeling it's a strange thing to say. 自分 (oneself) is the counterpart to 他人 (other people). I think that 自分で might have the meaning of 'by oneself', opposed to "have someone else do it instead" or "with some help from others." And traveling isn't something you'd make someone else do for you.
Maybe it can be interpreted to "I travel by myself (by my own means, I make the plans and reservations etc. by myself)" but I'm not sure. Unlike 自分で, this 一人で only states the number of people in the group you travel.
Just to put it out there : I've become way better at remembering the new stuff once I began reading staying with a solved problem and practicing the pronunciation a couple of times. Breaking down the sentence and getting a grasp of the words and how it all comes together and just saying it a few times really helps you remember it. It's all about making context.
If you say 一人でします you say "I'll do (it) alone." You say 一人にします, it means "I'll leave (you/him/her) alone." But what is this action of 一人する you're talking about?
します <- する (meaning: 'to do'), which is used to make new verbs from nouns or loan words. For example 旅行 = 'a trip; traveling', 旅行する = 'to travel.' 食事 = 'a meal', 食事する = 'to have a meal.' 発音 = 'pronunciation', 発音する = 'to pronounce.' シャンプー = 'shampoo', シャンプーする = 'to apply shampoo.'
You can separate these if you make the noun the object by adding を: 旅行をする、食事をする、発音をする、シャンプーをする. This time, 旅行を一人でします conveys the same meaning, but sometimes it changes the primary interpretation: きれいに発音します "S/he pronounces it clearly." 発音をきれいにします "I/It will make my/your pronunciation good/clear/beautiful." This is because (na-adj)+に+する is another special construction for suru-verbs, and きれいにする means 'to make clean/pretty'...
As far as i can guess, duo's reading robot recognizes standalone 一人 without any context as a surname. As far as i can guess, they are not correcting this horrible and infuriating mistake because this error isn't happening on duolingo part, AND the outsorced robot is also working fine - i mean, it reads sentences right, and japanese words without context do tend to have a multitude of meanings. If only duo could give that robot some furigana that only the robot would see... i really hate hearing ひとり as かずと, and match 描き（えがき） with かき
Why would "alone, one person" (一人) be the direct object of the verb "travel" (旅行する)?
The word "alone, one person" 一人 can't be what you travel (i.e. a route or area you travel). So it's not 一人を.
Instead, "alone, by myself" 一人で is something about how you travel (i.e. the way that you travel). For something to compare with, to make it clearer, another thing about how you travel might be "by car" 車で. ^^
ます is just an auxiliary verb. It is added to the end of a verb to add an air of politeness/formality.
し is the verb する (meaning "do") but this し is a non-finite form of it. This is a form that is used with many auxiliary verbs (such as with ます).
します = し + ます
旅行 is just a noun. It means "travel (travelling), trip, journey, excursion, tour"
旅行する = travel + do
旅行します = travel + do (polite/formal form)