I need a custom hidden field at checkout to capture the gclid

[chantelleripley]

Can you create a custom field called "gclid" in shopify?

I need to capture the gclid from all customers that checkout on my website

so that i can optimize tracking conversions for advertising

i don't have shopify +  is this an option i can self edit or pay someone to add to my site?

[PaulNewton]

You would use cart attributes,  and javascript to put the gclid id from the url into the attributes value. This has to be done in the /cart step BEFORE checkout so is only valid for the online-sales channel

https://community.shopify.com/c/shopify-design/cart-use-cart-attributes-to-collect-more-information/... 

If you need this customization then contact me by mail for services with detail.
ALWAYS please provide context, examples: store url, theme name, post url(s) , or any further detail in ALL correspondence.
Contact info in signature.

[gr_trading]

Yes @PaulNewton is right you can store the information in cart attribute which will not be visible to user.