asdoc tab using option sum error Stata

I am getting familiar with your stata command asdoc. Thanks for sharing this. However, I have encountered an issue. If I type

tab var1 var2 , sum(var3) means

I have my desired output If I type

asdoc tab var1 var2 , sum(var3) means

it does not work. It returns the error:

option sum() not allowed

Could you please help? Best regards, Antonio Lazzarino