Error "You do not have access" When Connecting to MFA

To resolve this issue, please try the following steps in order to see if the situation improves.

1. Clear Browser Cache and Cookies
Delete your browser's cache and cookies, then restart the browser and try logging in again.
2. Use Incognito Mode (Private Mode)
Open your browser's Incognito mode (or Private window) and check if the error occurs. If this resolves the issue, it is likely caused by extensions or the cache.
3. Use a Different Browser
To isolate the problem, check if you can log in using a different browser (e.g., Google Chrome, Microsoft Edge, Mozilla Firefox) than the one you are currently using.
4. Log Out and Log Back In
Click **Log Out** on the screen displaying "You do not have access" to end the session, and then perform the login procedure again.
5. Update Your Browser
Ensure that your browser is the latest version supported by Salesforce. If it is an older version, please update it to the latest version.
6. Check the Login URL
Check if you are accessing the correct login URL. If you are accessing from a bookmark, reconfirm that the URL is correct.

* Standard Login URL: https://login.salesforce.com
* My Domain URL: https://[MyDomain].my.salesforce.com

Reference : 

Supported Browsers and Devices for Salesforce Classic

Supported Browsers and Devices for Lightning Experience

Common multi-factor authentication (MFA) troubleshooting