Is there any way of not using my_init_method in the following code (that creates a custom post type)?

What is the error message being generated?

Also, to avoid conflicts, all custom Theme functions, classes, options, constants, etc. should be prefixed uniquely, e.g. using theme-slug.

It is highly likely that a generic function name like my_init_method is used by another Plugin or Theme. Try renaming it to mytheme-slug_init_method.

EDIT:

To implement, rename your function call from:

function my_init_method() {}

to:

function mytheme-slug_init_method() {}

Then, change your hook call from:

add_action( 'init', 'my_init_method' );

to:

add_action( 'init', 'mytheme_init_method' );