Issues With Creating A Datasource

I haven't tested your code but I would try doing some testing and attempt to narrow down which part exactly is causing the issue. For example does your code work fine if you remove all the parameters from the URL? And if you remove just the filter part? My gut feeling would look at the non-alphanumeric characters in your filter and there might be differences between how REST calls work in PS vs Groovy. Perhaps they need to be escaped. You might also want to simplify your code, just for testing, in case there are issues with function parameters or the like.