Anyone considering a reseller SMM business needs to understand the difference between API-driven and manual order processing, because it shapes almost everything about how the business actually runs day to day.
An API-based panel connects programmatically to upstream service providers — the moment a customer's payment clears, the panel's system calls the provider's API directly, with no human step in between. Orders start within seconds to minutes, the reseller never has to manually action anything, and the business can run largely unattended once it's set up. The tradeoff is dependency: pricing, reliability and service availability are all inherited from whichever upstream providers the panel is connected to, and if a provider has an outage or price change, it flows straight through.
A manual panel (or a panel with manual-only categories) queues orders for a staff member to action by hand — sometimes because the service genuinely requires human judgment (custom comments, for example), and sometimes because the operator hasn't built or paid for an API integration for that service yet. Manual processing means slower fulfilment and requires actual staffing to keep orders moving, but it can also mean more control over quality for services where automation doesn't do the job well.
For a reseller specifically, an API-based panel with a white-label API of its own (letting the reseller's customers order automatically through the reseller's own branded site) is usually the more scalable foundation — it removes the reseller from having to staff order fulfilment at all, leaving them to focus on their own pricing, marketing and customer relationships instead. The main diligence item is understanding exactly which of the panel's own services are genuinely API-fulfilled versus manually queued upstream, since that affects what a reseller can honestly promise their own customers about delivery speed.