All roles can initiate a receipt. A shopper can only receive against orders they participated in (or were invoked in as the Prepared For). Requesters and Approvers have access to University activity.
Most common troubleshooting: Check their browser and be sure to use Chrome or Mozilla, which are recommended by the B2P software provider, Jaggaer. If they are on an Apple computer, Safari security settings can cause issues.
Other troubleshooting:
Use a laptop or computer. Phones and tablet versions of browsers may cause other issues.