I don't know what you are doing exactly. I pick one extraction of data
'Make API call to get detailed metadata for each channel
'Here also use Foreach loop for multiple API call
ch = "APILink" 'Here File Call From Server
rxfer.SetUrl(ch)
raw = rxfer.GetToString()
channelJSON = ParseJSON(raw)
' create a node for the channel and set its metadata fields
channelNode = CreateObject("roSGNode", "ContentNode")
channelNode.title = channelJSON.JSONField ' Here you write JSON Field name
channelNode.hdposterurl = channelJSON.JSONField
Here the REST API Documentation. Here the question of JSON parsing using Brightscript for Roku app
Here.