Write a letter that explains why you want the visa and how you meet the qualifications. You need to convince the Consulate reviewing your application why they should approve it. Include samples of your work, emails with clients, proof of payments etc.
500k baht is 41k per month for a year. They need to make sure you can support yourself with CASH or equivalent. This is a normal requirement for most countries visas and investments like stocks/crypto aren't cash. You could try borrowing against your stock and deposit 500k in savings.
Write a letter that explains why you want the visa and how you meet the qualifications. You need to convince the Consulate reviewing your application why they should approve it.