I'm advertising on Facebook and I have an ad set where after I increased the budget significantly, I've seen cost per purchase triple in comparison to the month before. Digging into the data I saw there was a clear decrease in the CTR trend from the day in which I increased the ad set's budget and also in the conversion rate from click to app install. Install to registration and registration to purchase conversion rates didn't show the same distinct trend of decline.
I'm having a hard time putting my finger as to the cause of this sharp increase in the cost per purchase of my ad set. I'd really like to learn and improve my knowledge because these cases are likely to happen to me again in the future.
So - Why in some cases does increasing the daily budget on ad set/campaign lead to increase in cost per purchase?