Issue with Native PDF input (Base64) in gpt-4o - Error: invalid 'input[0].content[1].file_data'

You need to send a data URI, not just bare base64.

Does the error text continue, with "Expected a base64-encoded data URL with an application/pdf MIME type (e.g. 'data:application/pdf;base64,SGVsbG8sIFdvcmxkIQ=='), but got an invalid base64-encoded value.