Belinda Allen has a great suggestion to Add Bar Code Field to Item Maintenance Ian Grieve and I agree that we should all vote for it. Follow the link from azurecurve to vote.
MS Connect Suggestion: Add Bar Code Field to Item Maintenance | azurecurve
Sales, Purchasing & InventoryDevelopment & IntegrationMicrosoft & the GP Ecosystem
Archived post from 2016. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.