You may face trouble with your Zoho Invoice account if you haven't confirmed it. But, your data would be absolutely safe with us. Once you confirm and validate your account, all the data would be fetched back to the account. If you still face any issue, you can uninstall and re-install the app again on your device.
To access your Zoho Invoice app, first you need to authenticate your registered email address. Please check your inbox and see if you received an email from Zoho to confirm and validate the same. If you find any trouble with logging into the Zoho Invoice mobile app, you could try accessing Zoho Invoice via the web-app (https://invoice.zoho.com). Use your email address (the one that you registered your account under Zoho) as the user-name.Use your email address (the one that you registered your account under Zoho) as the user-name to reset your password (check the steps).
Zoho Invoice FAQ