The weekly budget is always the priority. The AI calculates each day's budget from what remains of the weekly limit, divided by the remaining days that have a percentage in the distribution. The monthly budget is optional and works as a second-priority ceiling: it never increases spend, it only cuts when the month's total gets close to the limit. For the weekly budget, the Minimum is the guaranteed floor even in bad weeks, and the Maximum is the ceiling the AI can reach when performance is excellent. If the weekly or monthly limit is exceeded, all managed campaigns are set to the minimum budget until the next period. So if you fill in the monthly field, review it: a forgotten value there can cut your spend sooner than you expect.