Why am I not able to migrate some applications into Zoho Finance Plus?

Only admin users of an organization can migrate the individual application.

For example, you might be the admin user in Zoho Finance Plus, Zoho Books and Zoho Expense, but not Zoho Inventory or Zoho Billing.

Service Administrators are responsible for managing user access for your organization. So, contact the individual application admin to add you as an Admin user to the respective application.