Could you please tell me how can I create a retainer invoice from 1 selected article when my invoice includes several articles (I would like to exclude of payment other articles from the same invoice) ?

For example : 

I create an invoice that contains 7 articles. For the first moment, I would like my client to pay me only 50% from the 1st article.

Is it possible to send a retainer invoice that concerns only 1 article ?

Thank you very much in advance,

Kind regards