1. For making payments, I would need a certified developer account for usage in the actual production environment.
2. The individual merchants have to create a merchant account within visa and then all payments should be made towards those accounts and the merchants would receive it
I would also like to ask if it was possible to make payments to different merchants or merchant accounts in a single application (mobile). This could be done by selecting a merchant account ID within that application, then making that payment towards the ID, allowing multiple merchants to be able to use that application.
Thanks for being part of the community forum and for posting your question to us! When you are ready to promote your project, during this process, some APIs will need to go through certification then production, while other APIs can move directly into production. It's really dependent on the APIs that you use.
For payments, individual merchants don't have to create a merchant account within Visa to process a payment transaction. Depending on how you build the application, it could work both ways.
Please take a look at our payment methods category, I've included the documentation link below: