Why is that? Is seems to me that journey and travel (as noun) is kinda the same thing. https://dictionary.cambridge.org/pl/dictionary/learner-english/travel_2
I use the upward opening accent when using my phone or tablet and Duolingo has accepted it as correct. Have you tried this? I believe you can also simply type an "x" after the letter you wish to have an accent (so you would type "gx") and the program will recognize it.
If you have Android phone, you can install AnySoftKeyboard from F-Droid or Google Play Store. AnySoftKeyboard allows you to type in many languages.
After inatalling AnySoftKeyboard I recommend you to go to Keyboard/Input settings in your phone to enable Vibrations since it is disabled by default. Well, at least I like it when there is vibration on key presses.
For those who wants to understand why travel is not acceptable here : https://www.espressoenglish.net/difference-between-travel-trip-and-journey/
I understand that travel is more the concept, the idea, not the concrete thing. I mean... I don't know how to say. Just read this short article.