how to add weekdays multiselect field to a cart price rule?

[rams1311]

My coupon code should work only on selected days.. I am new to magento development.. Is there a guide to help me how to develop this..

[Tom Robertshaw]

As you mention, this isn't custom. 

I think you would need to add a new extension with a custom condition. You could look through how the built in conditions are built to give you some guidance:

https://github.com/magento/magento2/blob/b2f688c6402289e4efb1e21fc894bc4a8d2a8be5/app/code/Magento/S...