Hi,
It seems you might have not got the settings right. Are you trying to set a min/max amount by category or by product?
If you want to set the min/max amount by category, here are the steps you should follow, in the plugin’s settings:
General > Amount limits > Minimum and Maximum
General > Amount types > Sum
The rest of the settings in General such as checkout options should be selected as per your requirement.
Then in the Amounts tab leave both Min sum and Max sum as zero.
In the Products, tab Enable the Per product category option.
Then in your WordPress dashboard go to Products > Categories and edit the first category (For example category A) in which you require a minimum amount as 2000 pesos and set the Min sum as 2000 pesos. Then edit the second category (For example Category B) in which you require the minimum sum as 1200 and maximum sum as 3000 and set the relevant values.
Once you follow this products in category A will require a minimum sum of 2000 pesos. Products in category B will require a minimum sum of 1200 and a maximum sum of 3000.