Updates multiple subscriber records in a single request using direct database writes.

Note: Unlike the single-subscriber update endpoint, this operation does not
run form pipelines, automations, or timing operations. It is a lightweight bulk field update.

Identifying records

Each item in the array must identify the record to update using one of:

• id: the numeric subscriber record ID
• mssys_idparam: an object of {fieldName: value} pairs used as the WHERE clause

Error codes