If your user role is set to Manager in your brand, you won’t have sufficient permissions to view the billing page. Please ask your brand admin/owner to change your role to Admin.
First, go to Settings > Users and then click Change role.

Select Admin and then click Change role.
Please note: Only the Brand Owner can change user roles.

Once that’s done, you’ll be able to access the Billing page from the MailBluster Brand > Billing section.