One thing that trips up even native Japanese speakers is the windows IME. It likes to change characters like spaces, dashes, alphabet letters and numbers to roman ones when you intend them to be Japanese "full-width" characters. In our office there, our address was often rejected because the final part describing the floor number should be "−４Ｆ" would come out of the IME as something like "-4F", "−４F", "-４Ｆ" (yes that last one is wrong).

The MacOS IME is much easier to use, and was the singular excellent use of the MacBook touch bar. It lets you pick the correct character, pick autocomplete suggestions, and convert between full-width, half-width, katakana, hiragana, etc.