One GET request to /v3/verify with the number and your API key; the key goes in the query string or an Authorization header.
Sign up, copy the API key from the dashboard, and make one GET request: https://api.veriphone.io/v3/verify?phone=%2B14169670000&key=YOUR_API_KEY. The key can also be sent as an Authorization: Bearer header. Give the number in international format when you can; if it has no country prefix, pass default_country as a two-letter code such as US, otherwise the country is inferred from the caller's IP. Add mode=current to resolve the carrier currently serving the number (10 credits instead of 1). The response is JSON; you are charged one credit only when status is "success", never for errors. There are no SDK requirements, any HTTP client works, and the docs include examples in curl, JavaScript, Python and more.
curl "https://api.veriphone.io/v3/verify?phone=%2B14169670000" \ -H "Authorization: Bearer YOUR_API_KEY"