MALFORMED_ID

A value supplied as an ID is not a valid Salesforce ID for that field.

Common causes

• The value is not 15 or 18 characters, often because of trailing spaces or truncation.
• A name was supplied where an ID is required.
• The ID belongs to a different object type than the lookup expects.
• A spreadsheet altered the IDs. Excel treats 15-character IDs as case-insensitive in lookups.

How to fix

• Use 18-character IDs in all files and integrations. CASESAFEID(Id) converts a 15-character ID in a formula.
• Check the three-character prefix: 001 Account, 003 Contact, 006 Opportunity, 00Q Lead, 005 User, 500 Case.
• Trim whitespace from ID columns before loading.