The reason why you can't login with your credentials is because you might have Two Factor Authentication in your Zoho account.
You need to generate an additional password that is going to be the one you set on ConnectMyApps, follow these steps:
1. Log in to Zoho at https://www.zoho.com/login.html
2. Click on CRM
3. Go to your usernames picture on top right corner
4. Click My Account
5. Click Two Factor Authentication
6. Click Manage Application Specific Passwords
7. Enter device or app name, then enter current password
8. Go to your Zoho application in ConnectMyApps and enter your Zoho password
Once this is done you will be able to add your Zoho app and create the workflow that will sync customers to your KashFlow account.
Please contact us if you need further assistance at http://connectmyapps.com/ContactUs