Firebase Dynamic Links Short Links API Returning 401

I'm using Firebase dynamic links short links API to shorten URLs in a Nuxt.js application. When I try to send a request to the API using Axios, it works and returns 200 when the application is initially started, but after some time (maybe a day or so), it starts returning 401 with the following response.

Request had invalid authentication credentials. Expected OAuth 2 access token, login cookie or other valid authentication credential. See https://developers.google.com/identity/sign-in/web/devconsole-project.

I have to restart the application to make it work again. Below are the request details.

Short Link API

https://firebasedynamiclinks.googleapis.com/v1/shortLinks?key=<key_of_my_firebase_project>

Request body (JSON)

{
    "dynamicLinkInfo": {
        "domainUriPrefix": "https://xxx.page.link",
        "link": "https://a.very.long/link"
    },
    "suffix": {
        "option": "UNGUESSABLE"
    }
}

Response (When it works)

{
    "shortLink": "https://xxx.page.link/XXXXXXXXXX",
    "previewLink": "https://xxx.page.link/XXXXXXXXXX?d=1"
}

What should I do to make sure I can always get a valid short link from Firebase?