Hi @dajw916 and welcome to the Dash community 
Nothing looks obviously wrong with the code. From the error message it seems like there is a problem with serializing the data to json format.
For debugging, you could try making a minimal example using a plotly sample dataset. More info on how to do that here: How to Get your Questions Answered on the Plotly Forum
I also recommend using the latest version of dash 2.13.0. And, since you are just getting started, check out Dash AG Grid instead of the DataTable. It won’t solve your problem because the data also needs to be in the same json format, however there are lots of cool features in AG Grid, and if you start with the grid, you won’t have to convert from DataTable later.