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1 Which documents to submit when I reapply for a standard visitor visa?
The same as before - employment contract for your new role plus payslips. If you re-apply immediately you’ll need to provide this for both old and new jobs (covering at least 6 months), however a rapid re-application, even with a new job, is likely to result in another refusal. I would recommend that you wait at least 3 months before re-applying.
2 How does one show that funds are available to you and exclusively for the purpose of travel?
The gold standard is to have the funds in an account in your own name, and to be able to show that you’ve accumulated them from your own income. If you have to use a sponsor, they need to provide full evidence of the source of the money (bank statements, employment contract/payslips, tax return etc). Do not be tempted to have a sponsor deposit money in your account upfront (see Should I submit bank statements when applying for a UK Visa? What do they say about me? and UK Visa Refusal: Provenance of funds/parking