Any suggestions to improve BuySell stock problem efficiency?

[mrapple2020]

I resolved the problem below. It seems this is (O(n)) = n^2.
In case you have a more efficient way to resolve it, kindly let me know. Thanks.
#################################################################################

#Imagine an array of ith element is the price of a given stock on day i.
#If you were only permitted to complete at most one transaction (buy one
# and sell one share of the stock), design an algorithm to find the maximum
#profit. Note that you cannot sell a stock before you buy one. 

#Input: [7,1,5,3,6,4]
#Output:5
#Buy on day 2 (price = 1) and sell on day 5(price = 6), profit = 6-1 =5.
#Not 7-1 = 6, as selling price needs to be larger than buying price.

def BuySell(array):
    
    #Retrieve elements, condition is that buy operation must happen before selling date
    best = 0
    for i in range (len(array)):
        for j in range (len(array)):
            if ( array.index(array[i]) < array.index(array[j]) ):
                profit = abs(   array[i] - array[j]  ) 

                if (array[i] < array[j]):
                   #Retrieve the best profit between buying and selling the stock
                   if (profit > best):
                        best = profit
                        return (f'Buy at ${array[i]}  Sold at ${array[j]}   Profit:${best}')
                        
    return

def main():
    array = [7,1,5,3,6,4]
    print(BuySell(array))

if __name__ == "__main__":
    main()