Looks like you have the same problem I had. Strangely enough after I managed to pair the first blind/button others paired fine even tho before they had the same problem.
Thanks to Andrew I did not give up, here is what I did.
Delete the all Ikea buttons and blinds from ST ( verify in the ST IDE that it’s clean)
Reset the blinds holding the two buttons on it till it starts blinking then open the battery compartment.
Reset buttons by pressing the pairing switch in the battery compartment 4 times and when it starts blinking pull the battery.
Unplug all IKEA Zigbee extenders.
Reboot the hub and give it good 10 min or so to get back on line.
Make sure you have the Veonua edge drivers installed (Ikea Window 1.1)
Pairing
Start with the blind.
Close the battery compartment.
In the ST app go to devices and start the pairing using Scan for nearby devices
Hold both buttons on the blind till it starts blinking.
When found, rename it to your liking and if you planning to pair more then 1 blind set the Group under settings to something else then 0.
Now pair the button
I did this without using the Ikea extender
In the ST app go to devices and start the pairing using Scan for nearby devices
Press the pairing button on the remote 4 times.
When found rename to your liking and then change the Group to the same number you set on the blind you just paired.
Even without setting the automated actions in the ST app under the button device you should now see that it works. It will change to color when pressed. and the indicator beside Stand by will change to amber.
Now set automated actions for both buttons to operate your blind.
This is what I did and it is working now
Paired other blinds since then without any problems.