What are the most common edge cases when mapping JSON to ISO 20022 for cross-border settlements?

"Modern web APIs rely on flexible UTF-8 JSON payloads, but ISO 20022 payment rails (like pacs.008) enforce strict SWIFT character sets, rigid string length limits, and complex nested fields for remittance info and party identification. Improper truncation or stripping non-ASCII characters often leads to AML false-positives, misallocated funds, or outright rejection by clearing networks. What are the most critical production edge cases when translating JSON payloads into ISO 20022 XML, and what are the recommended patterns for handling character conversion and field overflow?"