If possible, you should ask the company, or write in katakana so the client may be able to correct it later. In Japanese culture they usually ask how to spell someone's name because they think it's offending if they write it wrong. Also, since it is something that people remember as it is in their mind, the client may not find it wrong at a glance when he/she receives and checks it, then later others may find the mistake which may make the client feel embarassed later. gambatte!