Apple users
Open the chat you'd like to export
Tap the contact's name or group subject
Tap Export Chat
Select Without media
Save your file directly to your device (don't export to Google Drive)
Upload it to https://chatcharts.co.uk/products/chat-chart
Android users
Open the chat you'd like to export
Tap the three dots in the top right > More > Export chat
Select Without media
Save your file directly to your device (don't export to Google Drive)
Upload this to https://chatcharts.co.uk/products/chat-chart