Hi there and thanks for an informative publication. Digital marketing services are extremely important for promoting your online business. In addition to above info I would like to point that there are many marketing methods and specialities as SEO (Search Engine Optimization), ASO (App Search Optimization), SMM (Social Media Marketing), PPC (Pay Per Click) and few more. As a solo app developer I would say that ASO services are absolutely necessary to get more downloads of your application. There are plenty of good and free ASO services and I am currently using https://asolytics.com/. This tool collects statistics from millions of apps and helps me to manage the whole process of my app optimization. Also once you need to promite your online shop / any other commercial website - SEO service is a must to put your website on the top of google search results.