When you have a Studio flow, and you are able to trigger it once, but not for a second time, probably you have a stuck execution.
This could occur when you receive an event that Twilio wasn’t expecting, for example, you receive a message while you were executing a function, etc.
In this reference, you can learn how to find and stop these executions:
https://support.twilio.com/hc/en-us/articles/115016032048-Troubleshooting-Issues-with-Twilio-Studio
After that, check the execution logs to understand what caused the issue.
When this issue occurs, you receive the warning 81002:
https://www.twilio.com/docs/api/errors/81002
In the picture it is not possible to see very well the single and multiple entry feature that you are trying to build, feel free to open a ticket with Twilio if you need additional help.