Appeal deadline questions after an unemployment denial after 16 years as an electrician's helper

I got a denial letter last week saying I left my job voluntarily, but I was let go as an electrician's helper. My employer's version of events does not match mine, and I have emails that show it. If you have appealed before, what helped you prepare?

I printed my emails in order and wrote a one-page timeline. The hearing officer kept going back to it.