Python Dataframe: Create New Column Conditionally Using If Then Else Logic --> "The truth value of a Series is ambiguous"

I am using the following code to create a new column whose value is derived based on the values in two other columns of my Python dataframe.

# Create a list to store the data
MSP = []

for row in df_EVENT5_18['FLT']:
    if df_EVENT5_18['FLT'].str.contains('1234') & df_EVENT5_18['AR'].str.contains('ABC1'):
        MSP.append(29)
    elif (df_EVENT5_18['FLT'].str.contains('1234')) & (df_EVENT5_18['AR'].str.contains('ABC2')):
        MSP.append(25)
    else:
        MSP.append('')

# Create a new column from the list 
df_EVENT5_18['MSP'] = MSP

When I run the above code, I get the following error:

ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().