Hey Matt!
Based on how credit card authorizations are processed, you're not able to increase the amount of the order after that authorization has gone through. Ex: if a customer orders X from your shop and it costs $100, their card has been authorized to be charged $100. If shipping costs an additional $25m (and is not part of the original transaction), you're not able to increase the order to $125 afterward since only $100 was agreed to be charged. It's a security feature for the customer.
That being said, couple of ideas for you.
1. You can charge a higher shipping rate than what it will likely cost, then return the difference to your customer. It can be a great opportunity to surprise and delight your customer.
2. You can charge the cost of shipping outside of Shopify. For example:
- email money transfer
- manual transaction via your payment gateway
3. Or, once the original order has been placed and you've figured out the shipping, you could always create a new product in your shop that is the same price as the shipping and request that your customer places a second order on your shop for that 'shipping product'.
Hope that helps you out! Let me know if you have any questions.
Thea
Shopify Guru | thea@shopify.com
