Got a denial letter for unemployment, what now? after 18 years as an insurance claims processor

My claim was denied after 20 weeks of waiting, and the letter says I have a short window to appeal. I have read a lot of threads here and could not find my exact situation. 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?

Stay calm and stick to facts. Mine lasted about thirty minutes and felt more like a conversation than a trial.