If you are unable to synchronize your data between Synchroteam and ZohoCRM please check that the Two Factor Authentification has been activated on your ZohoCRM account. 
If so, then you have two options to properly synchronize your data :
1- Generate a specific password to connect with Synchroteam
2- Deactivate the Two Factor Authentification

It is also possible that you have reached the maximum number of authentication Token. In this case, you need to:
3- Revoke Auth Tokens

1- Generate a specific password to connect with Synchroteam

To do so go to your ZohoCRM's settings, in Security (1), check that the Two Factor Authentification is enabled, then click on the button "Manage Application Specific Passwords" (3).
Write "Synchroteam" as App Name and fill in your ZohoCRM password (4) and click on "Generate" (5).

Copy the generated password (6), go to your Synchroteam account, in Configuration > Integrations > Zoho, log out and log back in by pasting the password (without the spaces) (7).
You can know sy chronize your data with ZohoCRM.

2- Deactivate the Two Factor Authentification

On your ZohoCRM account go to your Security Settings (1) and click on the Two Factor Authentification box next to "Enabled" (2).
Fill in your password (3) and click on the "Disable" button (4).

3- Revoking Auth Tokens

Zoho CRM allows only a limited number of applications to connect to a Zoho account (up to around thirty connections).

If you have reached this number you can delete the authentication tokens that are no longer useful to you by going to your Zoho CRMC account -> "Sessions" (1), -> " Active Authtokens " (2).

Then select the unwanted tokens (3) and click on "Remove Selected" (4).

In the confirmation window click on "Proceed".

You can then log back into Synchroteam with your Zoho CRM account and synchronize.