[ HELP ] Amazon Automatic PPC vs Manual PPC ?

Hi folks!

I need some help on understanding how exactly these 2 PPC campaigns work because what happened it's almost exactly the opposite of what they told me and what it's shown in the FAQ.

At the beginning of the launch of my item I called the customer service and they told me that was recommended to launch an automatic campaign for about 2 months in order to collect enough dates about the keywords that let your item sells and then start a manual campaign with only the correct keywords in order to pay for only the words you are searched for.
I have used the automatic campaign for about 4 months and get a medium sales rate of 40 / 45 pieces a month, then I started a new manual campaign where I put only the keywords that made my item to be searched for and so to be sold: the results of the last month and half is that now my medium sales rate is less than 10 pieces.
Already asked if they see some error in my campaign and no,there isn't.
The selling rate of my item is costant all the year so no,it's not just a bad moment of the year.
Is there someone that have had my same problem?

Thank you!!

Did you run both manual and automatic campaigns at the same time?

FUTUR TIM said:

Did you run both manual and automatic campaigns at the same time?

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No,because I will pay 2 campaigns instead of one and because I will pay for the same keywords multiple times I think.
Do you think I will have to run both?Why?