By default, the first shipping method is selected when the list of shipping methods is displayed. However, if the shipping methods are reordered by shipping delivery function, the system does not automatically update the selection to reflect the cheapest option. This may result in a higher-cost option remaining selected by default.
Hi @Chi_n_Nguy_n_Van 
- generally, we display the least expensive shipping rate by default at checkout:
Could you let us know where you’re seeing this behaviour pop up? Is this in a output from a Function run or within an Extension UI? Happy to dig into this further to see if we can confirm expected behaviour.
Hope to hear from you soon!
Thank you for your response Alan_G.
As mentioned above, this behavior occurs when merchants use the Delivery Customization function to reorder their shipping options.
You can take a look at my record: https://youtu.be/jjvXRXy1FKw
In my record, when a buyer navigates to the checkout page, the first shipping option is automatically selected, which is why this behavior appears.
Thanks @Chi_n_Nguy_n_Van , that does definitely look odd, appreciate you sending that my way. Would you be open to sharing your extension code with me? We’d just need the basics in order to replicate what you’re seeing (so you can remove any non-essential code if needed there).
If you’d prefer to share that info with me via a private message, that’s cool too. I can set that up on my end if needed and reach out to you that way.
Hope to hear from you soon!
All matters should be clear based on the image provided. I am only using the payment customization function to reorder the shipping options from:
to:
As previously mentioned, Shopify selects the first shipping option by default. Therefore, in this case, the most expensive option (Shipping option 2) is automatically selected (instead of the Free shipping option)
I would simply like to confirm whether you or your team can improve this behavior—specifically, to ensure that the cheapest shipping option is selected by default after all delivery customization functions have been applied, or if there are any other recommendations or solutions.
Thanks for clarifying @Chi_n_Nguy_n_Van , just wanted to see if I could replicate the behaviour exactly. I’ll look into this for you on my end and share next steps once I have more info. Speak with you again as soon as I can.
Hi @Chi_n_Nguy_n_Van - just following up with some info here after confirming some things with the team. At the moment, the function doesn’t override the default selection behaviour, essentially, it just renames, sorts, or hides options depending on what you set.
The default behaviour is that if a buyer hasn’t yet made a selection, the selected option will be the cheapest of the options returned after your customisation has ran. However, if the buyer has made a selection, we’ll attempt to retain that selection after the customisation has ran, so I wonder if that’s potentially happening here. If not, let me know and I’d be happy to keep digging into this (if you’re able to share any repro code that would be super helpful as well if we need to investigate further) .
Hope this helps 
For my record, I accessed the checkout page for the first time using an incognito window, ensuring no previous session or local storage interference. However, I noticed that the first shipping option was automatically selected, instead of the cheapest shipping option, which I expected.
This unexpected behavior is the reason I’m reporting the issue to you and your team.
And here is my delivery customization function code:
function run() {
return {
operations: [
{
move: {
deliveryOptionHandle:
"65888ee8b6c7c5fe045f9b2e0e57eaf1-c3e090203786bc2e8bb3ca305acd7816",
index: 1,
},
},
{
move: {
deliveryOptionHandle:
"65888ee8b6c7c5fe045f9b2e0e57eaf1-6058796404e38ca1cabdcb4ec7f9ef8e",
index: 2,
},
},
{
move: {
deliveryOptionHandle:
"65888ee8b6c7c5fe045f9b2e0e57eaf1-0032a34caa898da7178d58bd34dfa31c",
index: 3,
},
},
],
};
}
with function input:
{
"cart": {
"attribute": null,
"cost": {
"subtotalAmount": {
"amount": "700.0",
"currencyCode": "VND"
}
},
"deliveryGroups": [
{
"deliveryAddress": {
"city": "",
"countryCode": "VN",
"provinceCode": null,
"zip": null
},
"deliveryOptions": [
{
"handle": "65888ee8b6c7c5fe045f9b2e0e57eaf1-80ec4a7496a2dd1c91ac653b79c996f6",
"title": "Free shipping",
"cost": {
"amount": "0.0"
}
},
{
"handle": "65888ee8b6c7c5fe045f9b2e0e57eaf1-0032a34caa898da7178d58bd34dfa31c",
"title": "Shipping option 1",
"cost": {
"amount": "10.0"
}
},
{
"handle": "65888ee8b6c7c5fe045f9b2e0e57eaf1-c3e090203786bc2e8bb3ca305acd7816",
"title": "Shipping option 2",
"cost": {
"amount": "12.0"
}
},
{
"handle": "65888ee8b6c7c5fe045f9b2e0e57eaf1-6058796404e38ca1cabdcb4ec7f9ef8e",
"title": "Shipping option 3",
"cost": {
"amount": "20.0"
}
}
]
}
]
}
}
Thanks @Chi_n_Nguy_n_Van , I’ll see if I can replicate this with your Function implementation there. I really appreciate you sending this our way.
Thank you for taking the time to review and follow up with me. If you need anything further, please don’t hesitate to let me know.
Hey @Chi_n_Nguy_n_Van - thanks for your patience. I believe I was able to replicate the behaviour you’re seeing here on my test shop with a text extension. I’ll do some further investigation into this on my end to confirm if this is expected behaviour and loop back with you once I have more info to share though. Speak with you as soon as I have that info on my end