Hi @Kashifm,

Thanks for sharing this with the Klaviyo Community. There could be a couple of reasons for this.

Firstly, if the send puts you over your sending limit for the month. If so, you will need to upgrade your account in order to dispatch this email.

Second, if you are sending from a disabled or suspended account. You will see if your account has been disabled or suspended by looking for a red banner at the top of your account when you log-in. 

If this is the case, you should reach out to support with the public API key of your account (please do not share that key here) asking for further information on re-activating the account.