Clarification on usage of pair_coeff & velocity create commands

refering to the couette flow example
1)
I wanted to assign different epsilon & sigma values for the wall and fluid molecules.
the input code i used was:
pair_coeff * * 1.0 1.0 2.2
pair_coeff 450* 450* 1.2 0.9 2.2

Getting error: Incorrect pai_coeff args

What i understood from the manual is that if use the pair_coeff a second time it would overwrite the existing ones. I am unable to figure out the mistake. Is there any other/better way to go about defining these values for different molecules.

2)
velocity flow create 1.0 482748 temp mobile

I could not make out what the value '1.0' and '482748' are for

Thank you for you constant support.

BR/Joseph

Comments below.

Steve

refering to the couette flow example
1)
I wanted to assign different epsilon & sigma values for the wall and
fluid molecules.
the input code i used was:
pair_coeff * * 1.0 1.0 2.2
pair_coeff 450* 450* 1.2 0.9 2.2

Unless you have 450+ atom types in your
system, the last command is bad. The 1st 2 args
are atom types. 2 or 3 types is usual.

Getting error: Incorrect pai_coeff args

What i understood from the manual is that if use the pair_coeff a
second time it would overwrite the existing ones. I am unable to figure
out the mistake. Is there any other/better way to go about defining
these values for different molecules.

2)
velocity flow create 1.0 482748 temp mobile
I could not make out what the value '1.0' and '482748' are for

The velocity command doc page explains it.