Hello Clara Fernández Forte,
Here some questions that maybe can help you:
Have you tried to debug the proces and find where the error is produced?
Could it be a standard error message, have you tried to find it using ctrl + f?
Could it be that it is the flow name without the part "Sample_"?
Hope this can guide you a bit,
Good luck!
You probably cloned 'Sample_ACT_CreateEmailFromTemplateAndThenSend' and used that as the basis for your microflow. In your microflow you will have an action that calls SUB_CreateLogItem. The TriggeredInMF attribute probably hasn't been changed, so has the example value from the sample microflow still.