ok, so i have the update, Huawei support informed that it can be an issue with unsuccessful or incomplete software upgrade. so they asked me to do few steps
1- turn off the phone
2- press power and volume up button for a bit of a while to enter into boot menu
3- select the option of Wipe System Cache
4- select Reboot
and check if its working. i did the above steps while getting connected with mobile data. had no Wi-Fi at work place and i felt it wasnt required.
found out i couldnt see that Wipe System Cache option. it was Wipe Data and install latest software & recovery . Huawei support was equally puzzled as i was. found out those wipe commands on different forums for Huawei Mate 20 pro but nothing for mate 20.
Once home, connected with Wi-Fi, after getting into the boot menu, i could see the wipe system cache, cleared that and rebooted as guided by huawei support. Google Pay still didnt work. i was told by Huawei support that someone will contact me within 24 hours as it has been escalated, with reference number provided.
tried again today with no Wi-Fi on, again found the same weird thing in boot menu, to re-install the latest software it shows the option but it asks to connected with Wi-Fi that i dont have at work. when i am home connected with Wi-Fi, i dont see this Re-install latest software option in boot menu. its like i am in a loop with Huawei support and with my phone.
i also got the reply from Google Pay, explanation of the error message but nothing new. so useless and pointless.