Change a Meta campaign budget (CBO)

Changes the daily or lifetime budget held at campaign level, which is how campaign budget optimisation (CBO) campaigns are funded: Meta distributes one budget across the ad sets. Use when: the campaign itself holds the budget. Check with meta_list_campaigns — a campaign with a budget shows one there. Do not use on a campaign whose ad sets hold their own budgets; Meta rejects it and the right tool is meta_update_adset_budget. The preview refuses before anything is sent. A campaign only holds a budget if it was created that way: the launch tools take budget_level: "campaign". It cannot be moved afterwards from here. Do not make large jumps casually: Meta re-enters the learning phase on big budget moves, and delivery gets worse before it gets better. Steps of 20% or less are safer. Returns the campaign read back from Meta so the new budget is confirmed rather than assumed. Amounts are decimals in the account currency; whole-unit currencies such as yen are converted here.