The short version
Animal Coins are Animal Hospital's currency, earned by completing patients and by Journal achievements — the wiki documents 10 Coins per entry, with combat entries like the Bed Monster's Hider and Mimic combinations paying the same. There is no code, trading, or AFK income system: the coin flow is shift performance plus Journal completion. The official listing confirmed the game's first x2 coins event for September 19-21, 2026; that window has closed, so current earnings run at the normal rate.