Calling checkout from external Button

I have thoroughly read the support docs on this subject and have tried to implement http://wpstripe.net/docs/misc/calling-stripe-checkout-externally/

I have also read this post on the forum where a fellow user was having the same problem. https://ww.wp.xz.cn/support/topic/calling-the-checkout-form-from-a-custom-button?replies=10

Again I have tried following the advice but this does not solve the problem.

Using shortcodes with standard stripe button works so everything is functioning fine. (see test page below)

http://bigthinkingonline.com/test-pay/

I want to call the stripe checkout from a custom button. I have assigned an id of my_custom_button as shown in the example to an image and then tried calling the checkout on click of that id but nothing happens.

I am not an experienced coder so if you could explain step by step where I have gone wrong and what i need to that would be great.

Thanks in advance

https://ww.wp.xz.cn/plugins/stripe/