If your customer is unable to add a product to their subscription, it may be due to the following reasons:
- You have not enabled the setting to allow this. You can enable this setting in the Subscriptions admin in Settings > Customer portal.
- The customer is using a currency different from your store's default currency. Customers can only add a product when they have purchased the subscription in the same currency as your store.
- You have made phone numbers required in the Shopify checkout, and the subscriber does not have a shipping phone number in Bold Subscriptions. To resolve this, add a phone number in the customer's Address and shipping information in the Subscription admin. For detailed instructions, please visit Troubleshooting Subscription Error Messages.