I have been seeing some users facing this issue, for this reason I am writting this blog.
When creating a shopping cart as operational purchaser (role /SAPSRM/OP_PURCHASER), where shop one screen is available, end user is able to see the "Note to supplier" label, but text box is not displayed.
As of SRM 7.01, it is required to activate business function SRM_CONT_IMPR_1.
This business function will make available switch SRM_701_KEYBOARD_NAVIGATION, that after activated will make "Note to supplier" text box visible to end user in shop one screen.
Following SAP Help link provides more information about switch SRM_701_KEYBOARD_NAVIGATION: