Check File Upload REST API in SOAP UI

Are you using the attachment tab in your POST request?

For a project I have I added a groovy step to encode an attachment to use in the body of my POST request

// Set results file path
def groovyUtils = new com.eviware.soapui.support.GroovyUtils(context)
def projectDir = groovyUtils.projectPath
folder = projectDir+"\\Results\\";
resultFile = context.testCase.getPropertyValue("TestResultsFile")	
if (resultFile != '') {
	resultFilePath = folder + resultFile
	testRunner.testCase.setPropertyValue("resultFilePath", resultFilePath )
	
	// encode file
	ResultsPath = context.testCase.getPropertyValue("resultFilePath")
	
	def inputFile = new File(ResultsPath)
	String encoded = inputFile.bytes.encodeBase64().toString()
	testRunner.testCase.setPropertyValue("EncodedFileRequest", "$encoded" )
	
	// get request
	def request = testRunner.testCase.getTestStepByName( "AttachmentContentRequest" ).testRequest
	log.info request
	// clear existing attachments
	for( a in request.attachments ) {
	 request.removeAttachment( a )
	}
	
	// get file to attach
	//ResultsPath = context.testCase.getPropertyValue("resultFilePath")
	def file = new File(ResultsPath)
	log.info file
	if ( file == null) {
	 log.info "bad filename"
	}
	else 
	{
	 // attach and set properties
	 def attachment = request.attachFile( file, true )
	 //attachment.contentType = "application/octet-stream"
	 attachment.contentType = "base64Binary"
	 attachment.setPart( "Message" )
	}

}else{
	testRunner.gotoStepByName("Loop")
}

Then pass the values that are need in the attachment tab. The image of from SoapUI Pro but it also works with the non pro