I think senior members can relevant to you and interpret it better for you :
3.1.5. Under paragraph 1(n) of Appendix FM-SE the gross amount of any cash income may be counted where the person’s specified bank statements show the deposit of the full net amount which relates to the gross amount shown on their payslips (or in the relevant specified evidence provided in addition to the specified bank statements in relation to non-employment income). Otherwise, only the net amount shown on the specified bank statements may be counted. Those wishing to rely on cash income to sponsor an application subject to the financial requirement may need to change the way they manage their money and bank the full net amount so that they can then rely on the gross amount of that income in sponsoring the application. Like the other evidential requirements of Appendix FM-SE which seek to maintain the integrity of the system for all genuine applicants and sponsors, it is important that those wishing to rely on the gross amount of their cash income from employment corroborate this income through their bank statements, as well as the required payslips and employer’s letter.
Example
The prospective sponsor of an application for entry clearance as a partner is in nonsalaried
employment with a construction firm in the UK. He is paid weekly in cash and
receives payslips showing this net income, together with the gross amount and the
correct deductions for tax and National Insurance. He currently deposits around half of
his net income in his bank account each week and uses the remainder of the cash to
pay his rent and some of his living expenses. He will need instead to bank all of his net
income each week so that this income is reflected in his bank statements for a period of at least 6 months prior to the date of application in order to be able to rely on the gross amount of this employment income in sponsoring his partner’s application. Failure to do this would mean that the unbanked cash income could not be counted towards meeting the financial requirement.
https://www.gov.uk/uk-family-visa/proof-income
https://www.gov.uk/government/uploads/s ... rement.pdf