Control of Velux from third party controllers has always been a thorny question.
Here are number of work arounds:
1. KLF 200 - best used with a KNX relay as its hard to get the short/long commands on a blind actuator to work in the right way. 3 options- relay for up, relay for down each from there own push to make KNX button and a third button that pulses both to close. OR change the KLF200 to signal mode to “use of one entry” then one keypad button can trigger one relay and it will cycle through open>stop>close>stop one each pulse
2. replace the velux control board with one of these but it’ll void the warranty. http://www.techniline.com
Neither solutions are ideal, but have been made to work.
Click here for the KLF 200 Manual
Control of Velux