Mainnet is the live blockchain where transactions involve real value. A testnet is a parallel network with worthless tokens, used to deploy and test contracts under realistic conditions before release.
A contract cannot be quietly fixed after launch, so the testnet is the last place where mistakes are free. Skipping it means debugging with user funds.
We run the full flow on a testnet with the real integrations attached, invite the client to try it with their own wallet, and only then deploy to mainnet with a documented rollout and monitoring in place.