Go to your OVH customer area, select your domain name, click on DNS Zone, then add an entry. Click on the CNAME field.
xyz.my-example-domain.com. 10800 IN CNAME custom.metaffiliation.com.
In the Subdomain field, enter the 3 letters that our system has randomly generated.
On the TTL drop down menu select Custom and enter 10800 seconds.
In the Target field enter the value custom.metaffiliation.com. (the dot at the end must be kept)
Click on the Next button, check the information and validate.