Please see the below image for reference. I have a shipping app set up which adds greyed out text below the shipping method title. How can I do this for shipping methods created within shopify itself and not on an app or can some suggest an app I can use to do this? (The app for DPD - Classic generates pricing from DPD) I would like royal mail to be a fixed price.
Customizing descriptions is currently not something that can be done within Shopify's native shipping rates system. It does require the use of an app. With Intuitive Shipping, you can create custom descriptions and custom delivery times so customers see exactly what you want them to see.
At this time we don't have an integration with Royal Mail for live shipping rates. We may offer an integration in the future. However if you're just using flat rates for your checkout, you can set up a custom service shipping method within Intuitive Shipping and call it Royal Mail (or whatever you like), then set the rate to whatever you want, along with your custom description and delivery time.
Intuitive Shipping is free to use in Setup & Testing mode, so if you're interested in trying it out, you can install the app for free, set up the Scenario and run some test calculations without having to select a billing plan. This will allow you to see if it's a good fit for your store.
Please note that to use Intuitive Shipping - or any third-party rate calculation app - Shopify requires that you enable their third-party carrier-calculated shipping rates feature. This feature is $20 USD per month. If you change your Shopify billing to annual, they will add the feature at no additional cost (plus they will reduce your billing plan by 10%). If you're on the Advanced plan or higher, this feature is already included and activated by default. If you're already using an app for DPD, it's likely you've already enable the feature.