Warning: Undefined array key "billing_information"

$inline_form = isset($pane_form['add_payment_method']['billing_information']['#inline_form']) ?? $pane_form['billing_information']['#inline_form'];
the above line in previous patch will assign a boolean (true or false) to $inline_form instead of the expected form array. Hence it wont fix the original issue.

Attaching new patch for the same