If that person who is a yr friend, or just you are his/her's fan,
ごめん(なさい)。既に寝てしまって(いて)、その配信は見られなかった(よ)。
Gomen(nasai). Sude ni Neteshimatte(ite), Sono Haishin wa Mirarenakatta(yo).Writing the characters in the first and second brackets also makes me a little polite.
Do not write the characters in the first and second brackets, and only add the last one will be most "frank".
(also only "ごめん。寝てて見られなかった(よ)。Gomen, Netete Mirarenakatta(yo). = Sorry, I couldn't watch since sleeping." enough)
if you are a woman, use "no(の)" or "wa(わ)" instead of last "yo", these words means just emotion stronger.
If you respect that person, this is the best than above.
すみません。既に寝てしまったので、その配信は見逃してしまいました。
Sumimasen. Sude ni Neteshimatta-node, Sono Haishin wa Minogashite-shimaimashita.Copy to below(delet brackets first), then click speaker icon.
http://voicetext.jp/Also "Google translate" has text reading function(by click speaker icon),
but intonation will be a bit unnatural. (Try it as comparing.)
And,
there are several words to use when apologizing as first saying word,
but in this case do not use "申し訳有りません。(Moushiwake-arimasen)".
http://cotoacademy.com/how-to-apologize-in-japanese-sumimasen/If btw friends case, you can use emoticons.
https://en.wikipedia.org/wiki/Emoticonhttps://en.wikipedia.org/wiki/List_of_emoticonsAlso if that small failed means just "Oops,",
you can use "てへぺろ" add last as embarrassment including a joke like this.
"ごめーん。もう寝ちゃってたわ。AA(below)てへぺろ"
http://aa-aa.com/kaomojiaa/kannjyou/tanosii/tehepero.htmlhttps://bangin.wordpress.com/category/slang/
