It just happened like a year ago. I created an insertion of my ecommerce and the first day I get my first sale. Then after 10 days the void. 5 usd-7 usd a day with a conversion campaign set to sales. Then downgraded to view content. But the results are always bad. Facebook give me a sale the first day to attract me to spend more but it's not like it should work. Here starts one hundred questions: the budget set don't give the pixel to learn? the problem is the targeting? the ad? the website? There is someone that can open me the mind on how to get first results?
It really depends on the niche and the product. Just make a deeper analysis of what have worked and what haven't. The daily budget is low, though I am sure that you have gathered enough analytical data.
The pixel will learn, it just needs some time and roughly a couple hundred dollars to work with before it gets decent data to work with. The other factors that go into it are things like Juherianto mentioned in his reply. Depends on how fast you want the data and the budget you have for the project.
You need to get more analytic data. Do thorough research about your customers and then launch a campaign accordingly.