The issue with your settings is this is not dynamic.
Instead of using the params. you could use the json body (or set it to raw body) and set the content-type header to application/x-www-form-urlencoded.
I prefer to use a plugin to convert a JSON to url params (JSON Serialize to URL query Plugin | Bubble … created by me for a case like stripe). It’s easier to manage in JSON. But this can be done without too.
Take time to search forum about Stripe array. There’s already a lot of solutions.
The main issue with a lot of solutions is the incremental array numbering that cannot be done easily with Bubble. The plugin take care of that.