Costs incurred by your business in the set-up or ongoing use of software or apps can be expensed (e.g. the cost of using earnr to manage your finances and tax).
Most software products and services are paid for via a subscription, this could be a web based app (e.g. Canva), a mobile app (e.g. earnr!) or a specialist software package (e.g. Adobe Creative Cloud). The subscription fees for an app used to run your business can be expensed.
Other software products are purchased for a one off fee, some useful mobile apps cost less than a pound, others such as Final Cut Pro, cost hundreds of pounds. You can expense the cost of purchasing an app for your business.
You may even incur costs to develop your own app or software, or perhaps configure a software tool for your business. These costs are less common for small businesses but can be expensed too.