Welcome to the community.
I am not familiar with interflex package. Two things you can check
- Make sure df_1890v2 is a dataframe (using command class(df_1890v2)) and it has at least 3 columns, "has_chapter", "share_sc_ten", "share_white" (usng command names(df_1890v2))
- For estimator, you use the option "raw". But, the package manual says, it can be one of the following: "linear", "binning", "kernel" or "gam"
You may consider presenting reproducible example by following FAQ: How to do a minimal reproducible example ( reprex ) for beginners . It will help people to think and solve the probelm efficiently.