UK Spouse visa, financial requirement is set to increase from net months from £18,600 to £29,000 and from £29,000 to around £34,500 expected to happen in late 2024 and from £34,500 to £38700 is expected to happen in early 2025. Usually, applicant would have to provide 6 months along with payslips, employer letter, bank statement showing deposit into account, if they have been employed with same employer for at least 6 months, however things get more completed once you would have switched from employment to self-employment during the last 12 months. For instance, if A is preparing application for UK spouse visa and were employed for 9 months and then become self-employed for the remaining 5 months, your income from both can be considered together to meet the financial requirements, provided you can produce payslips and bank statement showing evidence of employment and Self-Assessment tax return to other relevant documents to demonstrate earning.
To apply for UK spouse visa, off course all the income must be earned lawfully and make available all the relevant documents for employment and self-employment. Details guidance can be found at Gov UK website https://www.gov.uk/government/publications/financial-requirement-caseworker-guidance.