I am having some trouble sending emails using workflows
Hi @Swadhin_Ghosh,
When you click “Occurred 1 time in the last week”, you’ll be taken to an explanation of the error. If you can’t make sense of it yourself, please share a screenshot of what’s displayed in the “Event” column.
Best regards!
@Swadhin_Ghosh I’d recommend following the exact same suggestion as shown in the screenshot 
This is a case where the information is not shown in the frontend and HubSpot support can dig in the backend to provide an explanation. You should get a resolution, I’m sure of that.
If you want others to find these steps for troubleshooting, you can help them by marking my previous reply as an accepted solution.
Have a great day!