The short version
A recorded payment and an allowable tax expense are separate decisions. Keep enough detail to explain the business purpose.
Check HMRC guidance
HMRC explains allowable business costs at https://www.gov.uk/expenses-if-youre-self-employed. For mixed spending, only the business part of an allowable cost is claimed. Different rules can apply to assets and simplified expenses, so check the guidance for the particular cost.
Keep the allocation you chose
In Money, To confirm opens the existing controls for private use, disallowable treatment, business and property assignment. Split keeps separate amounts and categories within one payment. Review the saved allocation before changing it.
Review before filing
A suggested category needs your confirmation. Inspect grouped previews before applying a decision and use the 7-day undo when needed. Keep your supporting evidence and open Tax separately to review the update figures. Start with SimpleTaxFlow: £1 + VAT/month for 6 months, then £5 + VAT/month.
Put this into practice
Follow the step-by-step SimpleTaxFlow workflow when you are ready to act.