1. Create Custom Connector by going to Data -> Custom connectors -> New custom connector -> Import an OpenAPI file

   

2. Give connector a suitable name and select the Math.swagger.json and click continue

   

3. Click Create connector

   

4. Go to Code (Preview) -> click on Upload -> Select the Code.cs file

   

5. Expand the dropdown and select all the 3 available actions

   

6. Update connector

Now, your custom connector is ready!

More Details: https://parthbhaidani.com/2021/09/19/power-automate-flow-supports-c-sharp-code/