Open Snapchat and go to the chat with the person
Send a Snap, not a chat message
Make sure the Snap is unopened and sent within 24 hours of the last Snap exchange
Ask the other person to send a Snap back
Repeat daily to rebuild the streak
Check that both of you are using the latest version of Snapchat
Make sure your internet connection is working
If the streak disappeared recently, use Snapchat Support to request a streak restore
Open Snapchat settings
Tap Support
Tap I Need Help
Search for Snapstreak
Submit a streak restore request if available