It's now possible to update the warning message displayed in the checkout when a manual code is entered, is valid but has not met the required configured discount settings.
Navigate to 'Settings' -> 'Checkout' -> 'Checkout language' and click 'Edit checkout content'.
Click the 'Checkout & System' tab, and scroll down until you see 'Checkout general errors discount'.
Proceed to update the 'Additional requested discount code discarded' value.
If you want to translate this message into multiple languages, you can use the 'Translate & Adapt' app
Within 'Default theme content' -> 'Checkout and system', navigate to the 6th page.
Select your language and apply the desired translation.