Generating S-Function gives ERROR with Variable Size Signal

I am trying to generate S-function for my model and it is failing with ERROR as Support for Variable Size Signal is Turned Off.

However, I dont see the option to enable that Option for generating S-function. I have already tried the following:

1. Setting Model Referencing > Propagate sizes of Variable-size signal to During Execution.
2. Selecting Variable Size Signals in Code Generation > Interface

I am not sure how I can enable Support for Variable Size signal for Generating S-function.

Attached is the screenshot of the Issue.