Recommended path
Serve a server-rendered web application whose forms and links are handled by a same-origin BFF. The BFF holds the developer-app credential and issues POST /v1/payments after the customer completes checkout on your pages.
Developer preview API v1
Sandbox only. No real funds moved. No production access is granted here. Access requirements
Web + BFF
Server-rendered pages submit to a same-origin BFF that holds the credential and creates payments without exposing a secret.
Serve a server-rendered web application whose forms and links are handled by a same-origin BFF. The BFF holds the developer-app credential and issues POST /v1/payments after the customer completes checkout on your pages.
The browser only exchanges session cookies or same-origin form posts with the BFF. The BFF maps the signed-in merchant to merchant mer_01900000000000000000000000 and never forwards a live credential to the page.
Do not place a live credential in an HTML page, a static asset, or a customer-visible URL. Do not build a public client that calls the payment endpoint directly with a shared secret.