Hi Lalit, i think we need way more info to assit you.
1. Do you have autofill enabled on your wallet? Broadcasting is a paid feature on the Meta side, so you need to have the necessary funds
2. Does the message box say outside of the 24 hours?
3. Has the messaging template been approved?
4. Do all of these contacts have WhatsappID? Keep in mind when you import contacts the number is not imported as Phone, its imported as WhatsappID with the country code and no icons, for example not +50683333131, but simply 50683333131
Try checking all of those :)