Plaid Create a test Item

Use the `/sandbox/public_token/create` endpoint to create a valid `public_token` for an arbitrary institution ID, initial products, and test credentials. The created `public_token` maps to a new Sandbox Item. You can then call `/item/public_token/exchange` to exchange the `public_token` for an `access_token` and perform all API actions. `/sandbox/public_token/create` can also be used with the [`user_custom` test username](https://plaid.com/docs/sandbox/user-custom) to generate a test account...