Solved
You want your Resource to give just what the parameters are, not the values for them.
/{projectId}/newpricing/{pcode}/units
Then in the Test Requests themselves, you set:
projectId = ${Project#ID}
or
projectId = ${Project#InvalidID}
Any suggestions. I am using soapUI free version so wondering if there is another way to accomplish this where we can pass valid and invalid data at test case level to the same resource end point