A minimal reproducible example consists of the following items:
A minimal dataset, necessary to reproduce the issue
The minimal runnable code necessary to reproduce the issue, which can be run
on the given dataset, and including the necessary information on the used packages.
Let's quickly go over each one of these with examples:
If I recall correctly, regression analysis in R constructs dummy variables automatically so one does not create them manually as one used to do in SAS or SPSS.