Is commonly approved to signify at no financial Expense. Its use is acceptable in promotion or speech and its use is understood to necessarily mean no monetary cost. I might only change the use in a very circumstance where clarity and precision had been truly crucial, like in a deal. https://docs.google.com/document/d/e/2PACX-1vR1aRmbt0UmT4gxVq4IXbfDVfh2KrMfGfIz30gs2kLcIKk8h4EVktV5g2U8cNCzOTBSOZHhUqlkGaRY/pub