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‘Sponsorship’ in the context of a UK Standard Visitor visa relates to providing funds and/or maintenance, and/or accommodation to the applicant. Anyone who is legally present in the UK can invite someone to visit them there. There are no minimum income or savings requirements other than an applicant showing they have sufficient and proportionate funds for the trip and/or the sponsor being able to demonstrate the ability to fulfil the commitment. To prove this, sponsors should provide evidence of their financial standing (6 months’ bank statements, proof of earnings such as employment contract(s) and payslips), approval from landlord if the accommodation is rented.
Sources:
Immigration Rules https://www.gov.uk/guidance/immigration-rules/immigration-rules-appendix-v-visitor-rules
V 4.3 A visitor’s travel, maintenance and accommodation may be provided by a third party where the decision maker is satisfied that they: (a) have a genuine professional or personal relationship with the visitor; and (b) are not, or will not be, in breach of UK immigration laws at the time of decision or the visitor’s entry to the UK; and (c) can and will provide support to the visitor for the intended duration of their stay.
Guide to Supporting Documents https://www.gov.uk/government/publications/visitor-visa-guide-to-supporting-documents/guide-to-supporting-documents-visiting-the-uk
See also related questions What supporting documents should I include in my UK visa application? and Should I submit bank statements when applying for a UK Visa? What do they say about me? and What details should a good cover letter contain to back up a UK Visit Visa application?