[Python] How should we take the sum of values in a column after grouping by a different column...

I am trying to plot a graph for to analyze if there's any relation between the available_days of a property and number of reviews for it. I have a dataset which has different unique property listings, available_days for each property, number of reviews for each property. I am trying to plot by grouping the data by 'available_days' and I need to count the total number of reviews for those properties. For example, if the available days are 25, then I need to take the sum of the number of reviews for all properties with 25 available days. I couldn't figure out a way to do this. I tried as below but it is not giving me the expected result.

available_days=listings.groupby(['availability_365']).count()
available_days=listings.groupby(['availability_365'])['reviews_count'].count()
available_days=listings.groupby('availability_365').agg('sum')
available_days=listings.groupby(['availability_365']).agg({'reviews_count':np.sum})


Here is the dataset I am referring to:

This is the desired output format:

Also, please suggest a better way of approaching this problem to plot the graph.

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