Call all Potentials with specific Lead Source

Call all Potentials with specific Lead Source

I'm trying to get my head around the API. I'm attempting to create a simple page where one of our suppliers can see the status of the sales leads they've passed onto us.

The basic logic is show all Sales Leads (Potentials) where Prospect Source ( Lead Source) = Supplier Name.

I've constructed the following but it's still coming back with all records.

https://crm.zoho.com/crm/private/xml/Potentials/getRecords?authtoken=AUTHTOKEN&scope=crmapi&criteria=(Lead%20Source:Supplier%20Name)

Any idea what i'm doing wrong?

I'm new to APIs so prob missed something obvious