The right way itsis always こんいちは、こんばん, こんばんは。with with the particulaparticle "HA, は"It; It's like that because atit's the old japaneseJapanese way to say "good day". the "ha / は" works the same as "is", like: "Anata ha, watashi ha" あなた「あなたは」, わたし「わたしは。meaning somehting」 meaning something like, "today is a good day" etc. afterAfter some time, it becomes together by the cloquial day by day slang and speakingfused in everyday colloquial language. Also, we should also dontnot forgot that "japaneseJapanese Kana" only represents "sounds of spelling". We are allowed to write こんばんわ、with with "wa" though but, but we need to check where we are using it. This way of using "wa" can be only toappear in informal textstext such as web chats, closerwith close friends, and some manga. For any document that is official or forwith strangers itsit's mandatory usesto use the formal way, with "ha" and preferenciallypreferentially using kanji with the particule.particle 今日は、今晩, 今晩は。.