If the error response is type json:
oModel.callFunction("/myFunction", {
method: "GET",
urlParameters: {
ID: myID,
},
success: oData => console.log(oData),
error: oError => MessageBox.error(JSON.parse(oError.responseText).error.message.value, { title: "An error occurred" })
});
If the error response is coming from a Gateway and has an XML body (link):
MessageBox.error(jQuery.parseXML(oError.response.body).querySelector("message").textContent)