Recharge products subscription add item in cart using ajax

Technical Q&A
1 
<script>
  $('#add-to-cart-button').click(function(){
    addItemToCart(949931647, 1, "1", "Months")
  });
</script>
<script>
  function addItemToCart(variant_id, qty, frequency, unit_type) {
    data = {
      "id": variant_id,
      "quantity": qty,
      "properties": {
        "shipping_interval_frequency": frequency,
        "shipping_interval_unit_type": unit_type
      }
    }
    jQuery.ajax({
      type: 'POST',
      url: '/cart/add.js',
      data: data,
      dataType: 'json',
      success: function() { 
        window.location.href = '/cart'; 
      }
    });
    window.location = '/checkout';
  }
</script>

{
“type”: “text”,
“id”: “var_id”,
“label”: “Subscription variant ID”
}

for more Help

https://support.rechargepayments.com/hc/en-us/articles/360008683774-Adding-an-item-to-the-cart-with-AJAX#:~:text=If%20you%20want%20to%20allow,properties%20to%20the%20Shopify%20cart.