The matter is that you promote a free service. In fact this is not free, we paid with advertising the service. A mandatory Adobe Spark logo and made with Adobe Spark ending frame is too much invasive to be used. My suggestion it to put some limits. Like 5 projects per month without Adobe Spark advertising, or an overall of 10 projects per user without the Adobe Spark advertising. This way you let small business do their work within a set limit and then decide to invest in the pro version when they scale to bigger projects or have more work to do