You may have to choose between different login methods. Here's a quick guide to help you choose the right one for you:
Log in with your company account
If you are an employee and you have company credentials (firstname.lastname@example.org + password) that you use to login to several corporate services such as your email account, you are likely to use them to log in to your enterprise app store.
Log in with email
If you are an external contractor, a client or a partner (ie you're not an employee of the company which invited you to the enterprise app store), then you probably don't have company credentials to access to the store. Use the classical "Email connexion" and use the password that you defined after receiving your email invite.
Still unsure how to log in to your enterprise store?
If you still have questions, please reach out to your IT support!