Issue with multiple sites deployment in Firebase - firebase

Question

I have an Angular web application called "my-app".
I created a project on Google Firebase and called it "my-app" as well.
I deployed the Angular application to Firebase project "my-app". As a result, a site "my-app-*****" appeared. My app was accessible on "my-app-*****.web.app" address.
Then I created the second site in Hosting of the same project. I called it "my-app-dev". It got an address but was empty because nothing was deployed yet.
I followed instructions from google: https://firebase.google.com/docs/hosting/multisites
And even one question on StackOverflow: Firebase hosting deploy to other site
I added targets and modified firebase.json. In the result, they looked like that:
firebase.json file content:
"hosting": [
{
"target": "prod",
"public": "www",
"ignore": ["firebase.json", "**/.*", "**/node_modules/**"],
"rewrites": [
{
"source": "**",
"destination": "/index.html"
}
]
},
{
"target": "dev",
"public": "www",
"ignore": ["firebase.json", "**/.*", "**/node_modules/**"],
"rewrites": [
{
"source": "**",
"destination": "/index.html"
}
]
}
]
}
.firebaserc file content:
{
"projects": {
"default": "my-app-*****"
},
"targets": {
"my-app-*****": {
"hosting": {
"dev": [
"my-app-dev"
],
"prod": [
"my-app-*****"
]
}
}
}
}
But I faced an error when I executed command firebase deploy --only hosting:dev
However, when I executed command firebase deploy --only hosting:prod, everything was deployed without errors.
As a result, I am able to deploy my project to "my-app-*****" site, but I could not deploy my project to "my-app-dev" site. I want both sites to use same built files, that is why "public" was pointing to the same directory "www". Both sites located in the same Hosting of "my-app" project on Google Firebase.
Can someone please help me and explain what have I done wrong?