I have encountered an issue with my website recently where, when adding some products to cart, I receive the next error: parameter missing or invalid(bad_request): required parameter missing or invalid: items
Thanks for reaching out. I understand this could be better, so let’s look at all the options here.
I checked your links and can confirm that the same thing happened on my end. Slim Double Belt Harness product yields mentioned error no matter which variant is selected.
Generally, this error occurs when you don’t submit a variant ID or quantity amount with your Add to Cart form.
There are a few possible reasons for this:
You might have badly-formed HTML in your customized template. You can check your HTML by submitting your code to the W3C Validator.
You might have tried hiding the default option for a product with only one variant by removing the dropdown menu or single radio button. You must replace whatever you have removed with a hidden field that will pass the variant ID of the first variant to Shopify.
Interestingly, if you head to collections and try the Quick Shop button, this product gets added to the cart without issues. This could indicate that the changes made to the product template may be the root of the problem here. However, it is easier to say after looking into the account and theme code.
We cannot look into account specifics via the Community for privacy and security reasons. However, assuming your store has enough complimentary design time left, our team may be able to look into this for you. Please reach out to our Contact Us page.
Otherwise, if you are using a paid third-party theme, feel free to contact the theme developer to see if they can complete this customization for you. Also, you can post a job on the Shopify ExpertsPage and see what feedback and quotes you get.
