We know the following are true:

We don't want to make mistakes with valuable crypto-assets. Cryptocurrency developers know this. Many of them choose to run a testnet blockchain separately from their mainnet blockchain. The testnet functions identically, but the assets tracked there have no value. This gives developers a sandbox to try things in without risking real-world consequences in the case of lost assets. (TL;DR: Testnet is blockchain for the sandbox environment, and not for production.)

You will be provided with a Custody Infrastructure sandbox environment (proxy, MCS, and cosigners) that runs on testnets. We call this Sandbox mode. This mode gives you a platform to develop with before running with real crypto-assets. All of your settings from the Sandbox can be easily implemented to your production system.

Your Sandbox runs your target software version. This is either the version you are running now, or, when planning an upgrade, the version you plan on upgrading to.

The environment is fully cloud-based, with no special hardware needed. We deploy it for you and then give you access instructions. After we hand it over, the environment is yours to administer and experiment with as you will. If you need any help using your Sandbox, contact support.

The Custody Infrastructure sandbox environment functions exactly like the mainnet production environment with the same Desktop GUI, the same SDK, the same login procedures and workflows.

Of course, sending testnet assets when you mean to be transacting with real funds is ill-advised. We have taken steps across the MPC desktop and mobile app as well at the API to make it clear when you are working in a sandbox environment. Our software knows when it is running in Sandbox mode and automatically displays indicators for you throughout the interface.

When running in Sandbox mode on the MPC desktop app, there is an indicator in the upper-left of the toolbar directly under the logo:

When working through a transaction, there is an indicator at the top of the New Transaction pane:

Transferring NFTs can also be tested in the Sandbox. We have an indicator in the transfer pane to prevent confusion:

You can use the mobile app in Sandbox mode. There is a Sandbox indicator that shows up whenever you are building a transaction:

All the API calls are identical for mainnet and testnet environments. The endpoint calls and returns are the same. There is no ever-present indication when you are working with a Sandbox environment.

However, we do have a special API call that will let you know if your current environment is a Sandbox: isTestnetAddress

This endpoint returns True if you are running in Sandbox mode.