When the destination is WhatsApp, the WhatsApp Number field shows the numbers already running in ad sets in that account, including regular WhatsApp Business (the app) numbers, not just the Page's default.

  • Create campaign: choose the Page, then the number. The list shows the numbers already running with that Page. If yours isn't listed, use Enter another number... and include the country and area codes (a Brazilian number without 55 gets 55 added automatically).
  • Duplicate (same account, another account, objective change or new campaign): the modal lists the Pages in alphabetical order and the numbers that have already run in campaigns on the destination account.

Meta checks that the number is linked to the Page: if it isn't, creation is rejected with instructions to connect the number to the Page. Ads Editor doesn't support changing the number of an ad set that is already running.