Why would you enter any letters in a field (box) that says '6 digits'?
Digits means numbers.
with lazada vietnam I've experienced the code verification, if I use a VPN. I disconnect from the VPN then try and no code verification prompt.
Are you logging in from a location other than your usual?
Also, if you can use the app, login through that. I reckon the code verification is less likely with the app.