Direct SMS Configuration needs to be done in two separate areas.
To install Direct SMS
- You can install the plugin in your CRM by using the below link
Installation link - https://marketplace.zoho.com/app/crm/direct-sms-for-zoho-crm

Review your details and press 'Continue'
Check to agree on the “Terms of Service”, “Authorize the access” and click 'Continue to Install'.
Then Choose Users/Profiles and click Confirm.
Install for admin only - The extension will be installed in CRM for only the users with the administrator profile.
Install for all users - The extension will be installed in CRM for all the users. Users need to have a Direct SMS account to use his feature.
Choose profiles - The extension will be installed in CRM for all the users.
Enter your Direct SMS username and password into the field’s then click 'Save.
To complete the configuration you will need Direct SMS account. If you do not have an account, you will need to sign up at https://www.directsms.com.au/
If you have a Direct SMS account already please follow below steps to get User Name and password
Go to Configuration> API Settings > Create a new key

Note: There are a couple of things to be aware of to create the API credentials.
The first is that the username must be all one word, all lowercase, and alphabetical only (no numbers or special characters).
The second is that the password must be mix numbers and letters but no special characters
Now, enter your API Credentials username and password into the field’s then click 'Save.
Congratulations, you have successfully set up Direct SMS for your Zoho CRM.