This plugin is creating multi coupons for multisite.

@dhruvsompura are the three webhooks all in the same Mailchimp account? If so, I think they will all be triggered, no matter which store the subscriber comes from. If so, that is why you’re seeing three emails being sent. The best option would be to have three separate accounts, one for each store so that the webhooks only are triggered when a subscriber comes from that store.
Alternatively, if you don’t want to use three accounts you can use a third party service like Zapier that can receive the subscriber information from Mailchimp, then fire off a specific webhook if the subscriber came from a certain store. So you would have Zapier check the Mailchimp subscriber information to see where they subscribed from (maybe from a tag or some other field), then send the webhook only if the subscriber’s source matches that store. Note: I haven’t tried this method before, so I don’t know how well it will work.

So, how i can change in code that if user sign up then only from that website i want to create coupon code and send mail to that user ? Because from multi site website we want to give discount on only one site.

Can i add condition on web-hook in this plugin ? i want to send request for only one web-hook on sign up.

It really doesn’t matter whether or not you’re using a multisite. The issue is that Mailchimp sends out to all of your webhooks anytime someone subscribes to your list. The data that the plugin receives doesn’t really tell it which site the subscriber is coming from so the plugin isn’t able to conditionally create the coupon code.

The best option in your case would be to split your Mailchimp list into several accounts with one webhook per account. Otherwise it will continue to create multiple coupon codes for each subscriber.