Download the MISMO Reference Model 3.6.2 XML schema (published October 2025) from mismo.org and identify the relevant DEAL container and transaction type for the exchange
Map LOS loan data fields to the MISMO Logical Data Dictionary (LDD) element names, using the MISMO Unique ID introduced in 3.6.x for cross-system entity correlation
Generate and validate the XML payload against the MISMO 3.6.2 XSD schema, ensuring required containers (DEAL, PARTIES, LOANS, COLLATERALS) are present and properly nested
Wrap the payload in the appropriate MISMO DOCUMENT_CLASSIFICATION and set the DOCUMENT_TYPE to match the transaction (e.g., LOAN_APPLICATION, LOAN_PACKAGE)
Transmit the signed XML over a mutually authenticated TLS channel to the servicer endpoint; capture any MISMO validation fault codes returned
Reconcile response data by matching the MISMO Unique ID back to internal loan identifiers and updating the LOS record accordingly
Known gotchas
MISMO 3.6.2 is fully backward compatible with 3.6.1, but not with 3.4 or earlier; many GSE integrations still mandate 3.4 for specific use cases such as DU submissions, so confirm the required version per use case before building the schema mapping
The MISMO Mortgage Compliance Dataset (MCD) v2.0, released December 2025, uses a 3.6.0-tied XML schema to replace the legacy LEF fixed-format file; mixing MCD and Reference Model versions in the same pipeline causes schema validation failures
Field names in the MISMO YAML/OpenAPI representation differ in casing and nesting from the XSD; do not assume the OpenAPI spec and the XML schema are structurally equivalent when building dual REST/XML integrations
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