D455 can't open left infrared stream by Python

[2486851695]

When I use the code "self.config.enable_stream(rs.stream.infrared, 1, 640, 480, rs.format.rgba8, 30)" to get the rgba stream from the left infrared camera,it will back an error "self.pipeline.start(self.config)
RuntimeError: Couldn't resolve requests",but I change the code to "self.config.enable_stream(rs.stream.infrared, 1, 640, 480, rs.format.y8, 30)",it will be OK.
That's why?My firmware version is 5.16.0.1,in Intel RealSense Viewer can get the rgba stream from infrared camera.

[MartyG-RealSense]

Hi, please try it without the '1' index number. The index number is only needed for differentiating between the left and right infrared streams. But when only accessing the left infrared sensor (which the 'RGB from infrared' originates from), the index is not needed. RGB from infrared is only supported on the left infrared sensor.

self.config.enable_stream(rs.stream.infrared, 640, 480, rs.format.rgba8, 30)