I am having the same issue Samsung Pay getting stuck on the secure keypad not opening without being able to proceed any further.
The phone is brand new as of about 2 weeks ago - S21, 5G - all apps and phone software is up to date. Tried phone restart and still no progress getting past the secure keypad in Samsung Pay. I even tried to open samsung pay through my bank provider's app - no luck!
My Samsung watch4 is on it's way and I would really like to utilise these card-free paying features on my phone and watch (when it arrived!)
Please help! Phone purchased in Australia via Telstra.