Flask session doesn't persist in cypress test

Flask application consisting of login and form works well manually. However in Cypress test session is not available and test fails. Any idea how to solve or debug this behavior?

I can see create project form displayed.

I can see Cypress test click on the "Create" button.

Then manual test displays expected message that project was created.

However automatic cypress test behaves as if session doesn't exist

app.py

@app.route('/')
def homepage():
    user = session.get('user')
    render_template('home.html', user=user)

@app.route('/login-test/<string:email_address>/')
def logintest(email_address):
    if (app.debug):
        userid = 1
        user = { "email" : email_address, "uid" : userid }
        session['user'] = user
    else:
        flash("debug is off, can't use testlogin")
    return redirect('/')

@app.route('/create-project/', methods=['POST'])
def createproject():
    user = session.get('user')
    if (user):
        flash("Project added successfully")        
        return redirect('/')
    else:
        flash("Session not found")
        return redirect('/')

templates/home.html

{% if user %}
<form action="create-project" method="POST">
    <input type="text" name="name" placeholder="Enter new project name">
    <input type="submit" value="Create">
</form>
<a href='/logout'>destroy session</a>
{% else %}
<a href='/login'>login</a>
{% endif %}

cypress test:

describe('Basic tests', () => {
    it('We will use test login to login user1', () => {
        cy.visit('/login-test/user1@test.cz/')
        cy.contains('destroy session')
    }),
    it('We can create project', () => {
        cy.get('input[placeholder="Enter new project name"]').type('ProjectNo1')       
        cy.get('input[value="Create"]').click().contains('Project added successfully')
    })
})