Issue
You may not be able to leverage or specify a Studio Flow to work with a phone number in the Ireland (IE1) region.
Product
Twilio Studio
Cause
When configuring the voice settings for an Irish phone number, you may notice that only one option (Webhook) appears in the A call comes in dropdown.

This occurs because Studio Flows are not yet supported in the IE1 region.
Resolution
Define a webhook to a custom application or backend server where it can fetch TwiML instructions to execute a desired function.
Additional Information
Only select products and features are available for use in Twilio Regions outside of the United States (US1) Region. Information regarding regional product and feature availability can be found at the following link: