Flaky tests due to network responses (?)

I have a test that changes the amount of 3 products in a cart (from 1 to 5) and checks the total, ... So far so good. However, it seems that my POST statements are not awaited correctly...

The code below works sometimes, sometimes it does not:

test.describe.configure({ mode: "serial" })

const changeProductAmount = async (
 page: Page,
 amount: string,
 itemCounter: number
) => {
 // Wait for the POST request that adds an item to the cart
 const [response] = await Promise.all([
   page.waitForResponse(
     (resp) => resp.url().includes("/store/carts") && resp.status() === 200
   ),
   page.getByTestId("item-amount-input").nth(itemCounter).fill(amount),
 ])
 if (!response.ok()) {
   throw new Error(`Failed to update cart product amount`)
 }
}

test.beforeEach(async ({ page }) => {
 await Signup(page)
 await SignIn(page)
 await AddToCart(page)
})

test("Change Cart Items", async ({ page }) => {
 await page.goto("/cart")
 await page.waitForURL("/cart")
 await test.step("Change Cart Quantities", async () => {
   // Initial Amount of 3 items
   await page.waitForTimeout(5000)

   expect(
     await page.getByText("2.553,46 €", { exact: true }).first()
   ).toBeVisible()

   await changeProductAmount(page, "5", 0)
   await changeProductAmount(page, "5", 1)
   await changeProductAmount(page, "5", 2)
   expect(
     await page.getByText("12.767,30 €", { exact: true }).first()
   ).toBeVisible()
 })
 })
})
```
I would expect the...
```
expect(
     await page.getByText("12.767,30 €", { exact: true }).first()
   ).toBeVisible()
``` 
...to work just fine, since I am awaiting the update calls in my Promise in `changeProductAmount`. However I often get the error:

```Error: expect.toBeVisible: Browser has been closed
```
I can see in the UI though that the test went through. I think I am checking for the price too fast and miss an await

I am new to playwright so thanks for any help