If you are not sure which argument values to apply, you may want to use the Analysis Wizard. In the category Filters you can select the analysis for IIR Filter. In the second step you can play around with the filter type, characteristics and parameters and immediately check the results. After Finish you can Open the created analysis object (from the context menu) and look at the FPScript code generated. Alternatively, you can convert the object into a formula and adjust the code directly.
An additional remark: From the parameters supplied in your example, you want to filter a signal sampled at 1 MHz. The low pass filter at 150 kHz will not be problematic since the normalized frequency will be 0.15. But the highpass at 300 Hz will cause trouble, normalized to the sampling frequency the cut-off will be at 0.0003, a value needing extremely high orders tending to unstable behaviour.