Scaling Crypto Payment Processing

I'm researching cryptocurrency payment gateways for an online business that may experience significant growth in transaction volume. Some providers seem suitable for small projects, but I'm not sure how well they handle larger numbers of payments and outgoing transfers. I'd like to find a solution with API integration, automated transaction notifications, payout management and a testing environment for checking everything before launch. Support for automatic conversion between cryptocurrencies, such as receiving USDT when customers pay in BTC or ETH, would also be useful. Has anyone worked with a payment gateway that offers these features? Which services would you recommend for a business planning to scale its crypto payment operations?