ERR_UNABLE_TO_LOCK_ROW on Salesforce: UNABLE_TO_LOCK_ROW Error. Root cause: Salesforce record is locked by concurrent update from another user or process. Common causes: multiple integrations updating same record simultaneously, user editing record while sync runs, workflow/process builder running concurrently, record locked by approval process, database lock timeout exceeded (10 seconds default). Step 1: Isolate SOQL Queries. In your Apex code, append the FOR UPDATE keywords to your target SOQL selection statement. This instructs the platform to wait until the primary lock is released. Step 2: Sort Inbound Bulk Data. When pushing data arrays via Manus or external APIs, sort your data objects sequentially by AccountId before executing the batch. This minimizes cross-thread competition on the same parent record. Step 3: Reduce Batch Allocation Size. Drop your automated API batch processing size down from 200 records to 50 records inside your integration platform configuration to reduce transaction runtimes.