You should have an acquirer bank first who is willing to work with you before you start Visa Direct integration and testing. You will need a sponsor (Acquirer bank), who can do settlement for you. Acquirer means banks who can accept payments. You will have to develop a relationship with visa acquirer banks, which will help you create an account to do settlement on behalf of your clients which has different bank’s issued cards.
When contacting a Visa licensed acquirer, make sure to tell them you're looking for a Visa Direct acquirer because not all Visa licensed acquirers are enabled to sponsor Visa Direct programs.
If you are not able to find an acquirer, please refer to this page - https://usa.visa.com/run-your-business/visa-direct/find-a-partner.html
Per your requirement, I recommend the Visa Direct API product, which is available for use globally. Here's the link to Visa Direct: https://developer.visa.com/capabilities/visa_direct