I would like to images to my checkout page (apart from our logo), however i cannot find the right .liquid file to edit in (Boost theme doesn't have a checkout.liquid for some reason). I have made a backup already and have some experience with editing code, but im just not able to find the right .liquid file. I'm using Boost theme. Here's the link to our product page if you need it. Thanks in advance!
Checkout.liquid is a file that can be enabled by merchants using the Plus plan.
If you are on that plan, talk to your account manager or support team to have it enabled. If you are not on that file you'll have access to the customisations made available in the admin, but not the layout file itself.
Customisations like that would require that layout file.
Without it you may want to look into some strategies of adding the supported payment methods earlier. For example if you're finding people are confused about a certain payment method just add that info near the add the cart button on the product page, and near the checkout button on the cart page. Probably worth adding a FAQ page as well that lists out the sort of cards/methods of payment you accept.
Be interesting to see if adding that increases the conversions.