As one of the security protocols, Visa Developer sandbox secures its connections with clients by means of Two-Way SSL (Mutual Authentication) method. Refer to the link below to quickly learn about how to get credentials to start building with Two-Way SSL.
Visit the Two-way SSL Guide to learn more.
Some Visa Developer APIs require an API Key-Shared Secret Authentication, which Visa refers to as x-pay-token. To invoke an API using x-pay-token, you will need an API Key and a Shared Secret, which is provided via the link below.
Visit the X-pay Token Guide to learn more.
Visa Developer also provides the “Hello World” sample code that aims to demonstrate the connectivity with the Visa Network using the Hello World API and using the authentication method - Two-Way SSL (Mutual Authentication) and API Key – Shared Secret (X-Pay-Token).
Once you sign in with your Visa Developer credentials., you can download these sample codes from the Project Dashboard > Assets.