If I understand the requirement correctly, you can call a Flow from your Power App (and pass in parameters) then in the Flow you can use the HTTP action to POST request with relevant parameters.
You can return the data to Power Apps with the HTTP Response action (Power Apps Response action doe not handle complex data types).
The HTTP Response action will required a JSON schema, but there is an option to build that automatically from a sample payload.
The return value of the 'Flow'.Run statement will be the JSON data. You can use a collection to get this and then display it on the page as required (e.g. in a gallery):
ClearCollect(colReturnedData, MyFlowName.Run(Param1, Param2))
Note that all the HTTP actions are premium so every user of your App will require premium licenses (per user or per app licenses).