"Radios" not creating multi options?
Your code still shows radio instead of radios for '#type' attribute.

$form['paymentMethodSelect'] = array(
    '#type' =&gt; 'radios',
    '#title' =&gt; $this-&gt;t('How would you like to make payment?'),
    '#default_value' =&gt; 'eft',
    '#options' =&gt; [
        'eft' =&gt; 'EFT (Electronic Funds Transfer)',
        'cc' =&gt; 'Credit Card',
    ],
);


Otherwise there is no other problem I see in your code.
Sample code from D.O

$form['settings']['active'] = array(
  '#type' =&gt; 'radios',
  '#title' =&gt; $this-&gt;t('Poll status'),
  '#default_value' =&gt; 1,
  '#options' =&gt; array(0 =&gt; $this-&gt;t('Closed'), 1 =&gt; $this-&gt;t('Active')),
);