I’m sitting on a sizeable Excel/CSV file filled with phone numbers and need a clean, reliable way to split the list into two groups: numbers that are registered on WhatsApp and those that are not. The end goal is straightforward data cleaning; once the job is done I should be able to open the spreadsheet and instantly see which contacts are valid WhatsApp users and which are not, ideally in separate columns or separate files. How you handle the validation is up to you—Python, Node, Google Apps Script, or a desktop utility are all fine as long as they can comfortably process a large dataset without manual throttling. Please avoid any approach that risks numbers being messaged unintentionally; a silent status check via the WhatsApp Business API, yowsup, or a comparable library would be perfect. Deliverable acceptance criteria: • My original Excel/CSV returned with two unmistakable groups: “Valid WhatsApp” and “Invalid/Not on WhatsApp.” • No data loss—keep every original column and row intact aside from the added validation status or separate files you provide. • A brief note on the method used so I can replicate or rerun it if needed. If you’ve handled high-volume WhatsApp validation before, that will help a lot. Let me know how quickly you can turn this around and any size limits I should be aware of.