500 (Internal Server Error) when I try to refresh token: Authorization code with PKCE extension

[angela_parga]

Plan

Free

Country
Colombia

Device

HP LAPTOP-O1445JB9

Operating System

(Windows 11)

My Question or Issue:
when the first token expires, I try to use the refresh token to generate a new one without needing to authorize the user again. But I get an error 500 (Internal Server Error) in the function in charge of making the POST request:

async getRefreshToken() {  

        try {

            const response = await fetch(tokenEndpoint, {

                method: 'POST',

                headers: {

                'Content-Type': 'application/x-www-form-urlencoded'

                },

                body: new URLSearchParams({

                grant_type: 'refresh_token',

                refresh_token: this.currentToken.refresh_token,

                client_id: clientID

                }),

            });

            if(!response.ok){

                throw new Error('Failed to refresh token');

            }

            const token = await response.json();

            this.currentToken.save(token)

            return this.currentToken.access_token;

        } catch (error){

            console.error('Error refreshing token:', error);

            this.redirectToauthorize();

        }          

    },
and here I store the token

currentToken: {

        get access_token(){

            return localStorage.getItem('access_token')

        },

        get refresh_token(){

            return localStorage.getItem('refresh_token')

        },

        get expires_in(){

            return localStorage.getItem('expires_in')

        },

        get expires(){

            const expiryTimeString = localStorage.getItem('expires');

            return expiryTimeString ? new Date(parseInt(expiryTimeString)) : null;

        },

        save(response){

            const { access_token, refresh_token, expires_in } = response;

            localStorage.setItem('access_token', access_token);

            localStorage.setItem('refresh_token', refresh_token);

            localStorage.setItem('expires_in', expires_in);

            const now = new Date();

            const expiry = now.getTime() + (expires_in * 1000);

            localStorage.setItem('expires', expiry);

        }

    },