ROS service: problem passing parameters

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My service file is as follows:

float64[] sample
---
float64[] classify_probs

When I try to pass a numpy array of type float64 to the server, It gives me an error which is:

in check_type
raise SerializationError('field %s must be a list or tuple type'%field_name)
genpy.message.SerializationError: field sample must be a list or tuple type

I understood that I have to pass a list or tuple, so I converted the numpy array to a list as

temp_sample = testData.tolist()

and now it gives me the following error:

_check_types
raise SerializationError(str(exc))
genpy.message.SerializationError: <class 'struct.error'>: 'required argument is not a float' when writing 'sample:

The tolist() method converts the numpy array to a list with nearest compatible python type (in this case, it is a float). My question: is it possible to preserve the float64 type when converting to a list?

I tried changing my service file to "float" and ROS is not allowing it. Only float32 and float64 are allowed. Any help in this regard is much appreciated.