@Bimala Shrestha Thanks for reaching out. I understand that you're trying to create a EventGrid subscription with destination as webhook endpoint. As Sander mentioned above EventGrid does a test on the first call to check out if you are the owner of the endpoint I see here the endpoint is https://email.figsflow.com/email-event-status/event.
Did https://email.figsflow.com/email-event-status/event. handle the validation payload and return a 200 status code?
figsflow seems to be a 3rd party SAS product - Proposal, Engagement Letter Software for Accountants | Figsflow
Could you please tell us how are you able to handle the validation payload sent by EventGrid?
For more information please refer: https://learn.microsoft.com/en-us/azure/event-grid/troubleshoot-subscription-validation