Is the registered capital part of what I pay OCC for a Thai company?

No. Capital is your company's own money, paid into its Thai bank account, and it funds the business. The package price covers registration work and government fees. At least a quarter of each share must be paid up at registration, and foreign-owned companies often have to show capital brought in from abroad (confirm the amount for your activity with your specialist).

Thailand company guide

Source: To set up a company in Thailand as a foreign company, One Start One Stop Investment Center (BOI)