There are several reasons why you are having login issues in ZonTools. Let us go over them and find ways how to resolve them:
he issues that I can think aside from email address is kung may technical issue.
Like API has been revoked or may mga bugs ganyan po-
you need to use for each Amazon account or Marketplace a unique email address.
You can have multiple Amazon Seller Central accounts under one ZonTools login and unified dashboard but the email address you use for each Amazon account needs to have PPC permissions.
You can keep multiple Amazon Seller Central accounts under one ZonTools login and unified dashboard but the email address must have PPC permissions for each Amazon account or Marketplace. Hence, you need to have one Seller Central account per unique email address.
Your login issue can be rooted to an API or technical issues from the backend and would only be resolved by notifying the Support team who then can inform the Dev team.