In Service Portal the option to add an attachment is not available when editing an item in the cart.
Steps to Reproduce
1. Navigate to the Service Portal
2. Add an item to the cart
3. From the portal view, choose Cart > View Cart
4. Select the Edit icon next to the item
Notice there is no attachment option. The attachment option is available only when using the Service Catalog.
This issue is fixed in the Cart v2 widget since Kingston:
There is no workaround applicable on earlier releases. Please review the Fixed In section to determine the latest available patch your instance can be upgraded to.
To schedule an upgrade, please visit: https://hi.service-now.com/upgrade_dashboard.do?sysparm_cancelable=true and select the release which contains the fix.
Please refer to the below KB article for steps to upgrade if required: https://hi.service-now.com/kb_view.do?sysparm_article=KB0541128
Related Problem: PRB831985