Settings API settings section not appearing

The settings API can be puzzling 😉

Replace:

do_settings_sections( 'ia_section_id' );

with

do_settings_sections( 'srchild' );

to display your defined settings section.

The general usage is:

do_settings_sections( $page );

where:

$page (string) (required)
The slug name of the page whose settings
sections you want to output. This should match the page name used in
add_settings_section().
Default: None

according to the Codex (here).