Layer 1: distinguish input issues from platform issues
Start with twenty to fifty random records. Manually confirm market, country code and fixed-line or mobile type, then reconcile each source row with the returned file by normalized number. If the sample and full batch fail in the same way, revisit input and rule interpretation. If only the full batch is abnormal, investigate truncation, encoding, deduplication and column shifts.
Layer 2: verify country codes and number format
Global services usually expect E.164 or a documented country-code format. Common errors include duplicated country codes, inappropriate trunk zeros, extensions in the main field, full-width digits and invisible spaces. Number length and ranges differ by country, so pilot each main market separately and follow the provider's preprocessing rules instead of applying one domestic cleanup rule globally.
Layer 3: inspect batch mapping and deduplication
Large uploads can fail because CSV delimiters, column order, headers or spreadsheet conversion differ from the specification. Scientific notation can alter final digits. Check UTF-8 encoding, hidden columns and merged cells. Confirm whether deduplication uses number alone or number plus country, and whether internal cleaning is unintentionally compounded by provider cleaning.
Layer 4: align definitions, freshness and permissions
Providers may define valid, disconnected, suspended and unknown differently, using live checks or historical inference. Compare documented meanings rather than assuming one local convention. For APIs, an HTTP success is not necessarily a successful business result: verify credentials, rate limits, batch maximums and callback reachability. Insufficient permission can appear as an empty list or generic error.
Decide when to rerun or escalate
If a correctly formatted control sample still conflicts with documentation, test a second independently sourced sample before rerunning everything. Freeze a baseline for regression. Give support sanitized examples, format, task time and status codes, and record whether the root cause was format, mapping, definitions or permission so the SOP can prevent recurrence.
