@David *********
That has absolutely NOTHING to do with your extension. The requirements for the visa are from the embassy, and are from the MFA. Immigration is a completely different government agency with completely different requirements. You're not applying for a visa, you are applying for an extension. You cannot just submit a simple document showing income. The ONLY things you can submit for your extension is
1) Proof of 800,000 baht in a Thai bank account that has been there for 2 months
2) A letter of certification of income from your Embassy in Thailand showing you make 65,000 baht per month