The 100-credit verification purchase is an upgrade exception, not the regular minimum for later top-ups. After upgrade, Manual, Scheduled, and Forecast purchases use their regular minimums: $7.50, R$15, or ₹300 before applicable tax.
Check whether you are in the upgrade checklist or Buy credits. The amount shown in checkout is the final payment, including tax. Selecting a verification shortcut during upgrade changes the top-up choice; it does not charge you by itself. If an amount shown in Billing conflicts with checkout, stop and report both amounts and currency to support.