Hi Sacha,
So sorry for the trouble here!
There is a limitation in our cart that prevents two coupons from being applied to the same order — and bundles are considered a coupon item, which is why you were bumping into this.
The best way to go about it is to make separate purchases — one for the bundle and one for the additional license.
Let me know if this does the trick! If the coupon does not work after this, please send us an email to support [at] theeventscalendar.com and we’d be happy to help you out.
Geoff