Using Square for selling online

I have removed Paypal as a useful selling tool for my online sale page as they have become just too greedy by far. I have searched for a simple alternative that is free to use, ie no subscription costs, and have found Square that I already use for a simple payment option. On that site which is created by another program, ie non Xero, it has just a single option to make payment for a known amount without any other options, such as having to choose from sizes of things.
To integrate a suitable button onto my fashion site I now need to be able to add the option of clicking on a size from anywhere up to 10 alternatives. I have found that in Xara I can add the html to place a simple no option purchase but can't figure out how to make a drop down box for choosing the options.
Can anyone suggest a way to do this

Can't even guess a solution without some reference to the code you have at present, the (Size, Price0 ranges and any other necessary detail.

A link to Square might help, particularly examples for multi-options code...

Acorn