sending sequential requests to a rest service using SOAP UI

We have a rest service to upload images, the images are sent in a sequential order. Below is an example of what I am attempting to send:

{
"parameters": [{
"attachmentType": "UserUpload",
"fileName": "odometer.jpg",
"userName": "X6TW6"
}, {
"attachmentType": "UserUpload",
"fileName": "screen_shot_LT_heatmap.jpg",
"userName": "RNLVX"
}]
}

The Rest Service is only picking up the first image, so I will need to create multiple requests, any ideas on how to sequentially submit requests ?