Change a campaign bidding strategy

Changes how a campaign bids: maximise conversions (optionally with a target CPA), maximise conversion value (optionally with a target ROAS), maximise clicks, or manual CPC. Use when: the user has said what they want to optimise for and, for a target, the number they want. Do not use when: the campaign is less than two weeks old or has fewer than ~15 conversions in the last 30 days — Smart Bidding needs data, and switching resets the learning period for about a week, during which cost per conversion usually gets worse before it gets better. Say that first. Before changing anything the tool checks two things. If the campaign is driven by a portfolio strategy it refuses, names the portfolio and says how many campaigns share it; changing what that portfolio targets is then possible only with portfolio_strategy_id passed explicitly, because it moves every campaign on it. If you ask for conversion-based bidding it checks that the account actually has a working conversion action, and refuses with an explanation if it does not. Moving one campaign between strategies is separate and safe for the others: attach_portfolio_strategy_id puts this campaign on an existing portfolio (from google_list_bidding_strategies), and detach_from_portfolio takes it off and gives it the strategy you pass. Neither touches the portfolio or the other campaigns on it. The preview shows the before and after. Read-back confirms what Google stored. If you are unsure which account, campaign or period the user means, ask them — do not guess ids or dates.