set up my shop for eCOM is an add on module. Please subscribe to the eCOM offering to enable from Back Office.
Login to Back Office > go to ‘Settings’ from the left menu > go to ‘Shop Settings’ > select shop in the ‘Select Store’ option
Enable Switch for ‘Enable eCOM Setting’ > click on ‘Save Settings’ button 
Shop will be enabled for eCOM billing and the E-com link will reflect in ‘eCOM Settings’ which you will provide to your customers.