Fetch API returning nothing - flask

Question

I'm using Flask to retrieve data from my HTML file. It seems that nothing is returned to python, and the POST does not even seem to be going through because none of the console.log statements in my JS are appearing in the console. I have followed this tutorial.
Here is my HTML/JS code:
<input id="textInput" placeholder="a tagline for an ice cream shop"></p>
document.getElementById('text-generate-button').onclick = () => {
parent.postMessage({ pluginMessage: { type: 'placeholder-frame'} }, '*')
submit_text();
function submit_text() {
var textForm = document.getElementById("textInput");
var toSend = { text: textForm.value };
console.log(toSend);
}
fetch('${window.origin}/text', {
method: "POST",
credentials: "include",
body: JSON.stringify(toSend),
cache: "no-cache",
headers: new Headers({
"accept": "application/json",
'Content-Type': 'multipart/form-data'
})
})
.then(function (response) {
if (response.status !==200){
console.log('Looks like there was a problem. Status code: ${response.status}');
return;
}
response.json().then(function (data) {
console.log(data);
});
})
.catch(function(error){
console.log("Fetch error: " + error);
});
and here is my python
######## imports ##########
from flask import Flask, jsonify, request, render_template, make_response
template_dir = '/Users/ericaluzzi/Desktop/idep/figment-MVP/'
app = Flask(__name__,template_folder=template_dir)
#############################
######## Example data, in sets of 3 ############
data = list(range(1,300,3))
print (data)
#app.route('/')
def home_page():
example_embed='This string is from python'
return render_template('ui.html', embed=example_embed)
#app.route('/text',methods=['GET','POST'])
def get_text():
req = request.get_json()
print(req)
res = make_response(jsonify({"message": "OK"}), 200)
return res