String.Contains Design script not working Revit 2020

[nathan.chapman]

I have a design script to convert text feet/inches to decimal inches that works perfect in 2021 and newer but 2020 seems to not understand string.contains or really any string. Is there something different in 2020? Below is my design script.

Here is it working in Revit 2021.

[Draxl_Andreas]

@nathan.chapman ,

i think you need the prefix DSCore.