Updating your theme to support Submarine subscriptions

The Shopify theme needs to be customised to support the functionality enabled by Submarine (eg by capturing customer subscription preferences on the product page or in the checkout).

No specialised libraries or APIs are needed to develop these customer flows - they can be built using the Liquid, HTML, CSS and Javascript typically used for the development of Shopify themes. Special behaviours (such as configuring subscription frequencies) are driven through the use of standard Shopify features like Cart Attributes and Line Item Properties.

Cart-level attributes

Subscription frequency (conditionally optional)

A subscription frequency must be defined on an order to trigger Submarine's subscription behaviour. It can either be defined as a cart-level attribute or as a line-item property.

The name of the frequency cart-level attribute is _subscription_frequency. When defined at the cart level, the subscription will apply to all subscription items in the cart.

Possible values for the cart-level attribute are a magnitude and a unit, separated by an underscore - for example, 7_days, 3_months, or 1_year.

Opt-in for all line items (optional)

When all items in a cart should be part of a subscription, it can sometimes be more convenient to flag that once, at the cart level, rather than individually for each line item.

The _include_all_items_in_subscription cart-level attribute serves this purpose. When present, there is no need to include any _subscription_line_item line-item properties - instead, all of the carts items will be automatically included in the subscription.

Push back date of first subscription order (optional)

Submarine's default behaviour is to start the subscription from the time of the original Shopify order. So, if the frequency is set to every one week and the order was placed on January 2nd, the first subscription order would be generated on the 9th, the second on the 16th, and so on.

Sometimes, merchants may want to delay the start of the subscription, which can be done via the _submarine_initial_scheduled_at cart-level attribute. This should be set to ISO 8601-formatted time that the first subscription order should be generated on, e.g. 2020-10-22T12:00:00Z.

Other attributes

Any other cart-level attributes will be persisted on future subscription orders if they are whitelisted by the Submarine configuration.

Line item-level attributes

Line item subscription frequency (conditionally optional)

If you'd like to define subscription frequencies at the line-item level, you can do that with a line-item property.

The name of the frequency line-item property is _subscription_frequency.

The possible values are the same as for the cart-level frequency attribute.

Subscription flag (required, depending on configuration)

Submarine offers two subscription line item configuration modes, depending on merchant requirements:

  • If a subscription frequency is present at the cart level, include all line items in the resulting subscription;
  • If a subscription frequency is present at the cart or item level, only include line items with a line-item property of _subscription_line_item set to true in the resulting subscription.

These options allow you to easily create subscriptions with "mixed carts" - that is, some subscription items and some one-off items.


Submarine can be configured to either group line items by their frequency when creating subscriptions, or create single-item subscriptions for each subscription item in the cart.

Shopify metafields

Submarine adds the following metafields to Shopify resources (all are namespaced under 'submarine')

Customer metafields

customer_payment_methodsjson_stringAn array of Submarine payment methods for the customer.

An example of the submarine.customer_payment_methods metafield:

  "data": [
      "id": "123",
      "attributes": {
        "payment_data": {
          "brand": "Visa",
          "exp_month": 3,
          "exp_year": 2022,
          "last4": "1797",
          "processor": "stripe"
        "payment_method_type": "credit-card",
        "status": "active"

Shop metafields

api_urlstringThe URL of the Submarine API to use.
customer_api_secretstringThe customer API secret, required when signing requests to the Submarine API.
subscription_frequency_optionsstringComma-separated list of available subscription frequencies, e.g. 4_weeks,6_weeks,8_weeks.
default_subscription_frequencystringWhich of the above values should be the default, e.g. 4_weeks.