HTTP: Industry standards for back responses to the client - node.js

Question

Hi all I'm new to web development so I'm developing a simple online recipe book to allow me to also learn node and angular in the process.
How ever I'm struggling with what type of responses I should send back to the client for success and fails, in the case of post requests, or delete requests.
Here's an example of an api POST access point:
app.post('/recipe/',(req,res)=>{
res.set({
'Access-Control-Allow-Origin': 'http://localhost:4201'
})
console.log("Recieved req at /recipe/")
if(req.body.recipe === undefined){
res.send("Request not filled. No recipe found");
}
if(req.body.ingredients === undefined){
res.send("Request not filled. No ingredients found");
}
//var r = new Recipe(req.body.recipe,req.body.ingredients);
mongo.addRecipe(req.body.recipe,req.body.ingredients).then((promise)=>{
mongo.getAllRecipeByName().then(promise=>{
console.log(promise);
});
res.send(promise);
})
})
Here's the code for mongo.addRecipe() so you know what's being returned in that promise:
async addRecipe(recipeName,ingredients){
if(ingredients == null){
return null;
}
if(recipeName == null){
return null;
}
var recipe = new Recipe(recipeName,ingredients);
if(recipe.getIngredients().length <= 0){
return null;
}
try{
const client = new MongoClient(this.uriString);
await client.connect();
const db = client.db(this.databaseString);
const recipeCollection = db.collection(this.collectionString);
var status = await recipeCollection.insertOne(recipe);
client.close();
if(status.acknowledge == true){
return status
}
else{
return status
}
//console.log(await recipeCollection.find({recipeName:recipeName}).toArray());
}
catch(e){
console.error("Failed addRecipe() params: "+recipeName+" "+ingredients+e);
return null;
}
//String recipeName List<String> ingredients
//creates connection with mongo database.
//add {name:'recipeName',ingredients:'ingredients'} to mongoDB
}
So as you can see some of my verification statements return null and then I'm sending null back to the client. Is this a mistake? In the case of success I am returning the massive object that's returned from collection.insertOne();
What should I be sending to the client in the case of success and failure that fits with the industry standards?