How to approach a correlated multiple time series problem

Hello I wanted to see if anybody had any recommendations on how to best approach this problem. I am trying to forecast seven different time series based on three years of data. Based on those 7 time series forecasts, I want to calculate how much our costs would be.

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[Example of the original dataset and its daily differences version](https://preview.redd.it/vzuljme5vo091.png?width=2046&format=png&auto=webp&s=6d7296d41ed6f75ef9d1771c972c679dbbbdf6c8)

* Time series 1: Daily number of users we verified (one time cost per user)
* Time series 2: Daily …

datascience series time time series