Introduction to Anomaly Detection in R with Exploratory

I am following your great tutorial about Anomaly Detection in R

In general, it works fine with the expample data provided in the tutorial. But I do encounter problems with my own data as follows

Converting from tbl_df to tbl_time.
Auto-index message: index = date
Error in mutate_impl(.data, dots) : 
  Evaluation error: Only year, quarter, month, week, and day periods are allowed for an index of class Date.

Although the variable “date” has date format like “2018-01-01”. Could anybody give me an advice on that?
Thank you very much.

Maybe the ‘date’ column is not Date or POSIXct data type? Can u share the screenshot of Summary or Table view?