I'm afraid you can't. Even if you buy VideoNFTizer Flex Contract without the Standard Version, you will not be able to login.
Here is why:
1. VideoNFTizer Standard is the main product which is either a Monthly, Yearly or One Time Subscription.
2. VideoNFTizer Flex Contract is an Upgrade or Up-sell which adds the Flex Contract features in your VideoNFTizer account.
3. Since VideoNFTizer Flex Contract is not independent, you will need to subscribe for the main product VideoNFTizer Monthly, Yearly or One Time subscription first. Else you can't login with only VideoNFTizer Flex Contract in your account.