Decipher the Message [Forum game]

Unfortunately you didn't do it in time....but....

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Inspector: Did you do it? If yes, what did it say?
You: Unfortunately no. Wir seid sorry.
Inspector: Das ist OK. I'll give you more 5 days.

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If it's unreadable for you, tell me and I'll retry to make another one but readable.
(The <- is 20+1-1 if it's unreadable for you)
DAYS LEFT: 5
ATTEMPTS: 3
LITTLE HELP: What's the l_tter of _ot_ssi_m? Use the alph_bet a_d n_m_er. +x-=- +x+=+ -x-=+ LAST of _l_h_b_t

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