ERR_FILTER_INVALID on Zapier: Filter condition invalid. Root cause: Filter logic syntax error or field reference missing Step 1: Open the Filter step and read the exact condition that is failing. In the Zapier editor, click the Filter step (it shows a funnel icon). The filter displays each condition as "[Field] [Operator] [Value]". Read each condition carefully. The most common cause of an invalid filter is a field reference that no longer exists — if the trigger app's field was renamed or removed, the filter condition shows the old field name in grey text with a warning icon. Identify which specific condition is flagged before making any changes. Step 2: Re-map fields that have been renamed or removed in the trigger app. Click the field selector in the failing condition (the left side of the condition row). Zapier will show a dropdown of all currently available fields from the trigger. If your original field is missing, it means the trigger app's API response changed — the field was renamed, moved to a different object, or removed entirely. Select the replacement field from the dropdown. If you cannot find the equivalent field, go to the trigger step → click "Test trigger" → examine the raw data output to find the new field name. Step 3: Check the operator is compatible with the field's data type. Zapier's filter operators are type-sensitive. Using "Greater than" on a text field will produce an invalid filter because text fields cannot be numerically compared. Using "Contains" on a number field will also fail. Match the operator to the data type: for text fields use "Contains", "Exactly matches", or "Does not contain"; for number fields use "Greater than", "Less than", or "Exactly matches"; for date fields use "After" or "Before". If the field type changed in the trigger app, you may need to change the operator. Step 4: Test the filter with a real trigger event. Click the trigger step → click "Test trigger" to load a real recent event. Then click the Filter step → click "Test & Continue". Zapier will evaluate your filter conditions against the real test data and show you exactly which conditions passed and which failed, with the actual field values displayed next to each condition. This is the most reliable way to confirm your filter logic is correct — do not rely on manually entered test values, as they may not match the real data format. Step 5: Simplify complex AND/OR logic by splitting into separate Zaps or using Paths. Zapier's Filter step uses AND logic by default — all conditions must be true. If you need OR logic (any one condition being true should allow the Zap to continue), you cannot achieve this with a single Filter step. Instead, use Zapier's Paths feature (Professional plan): create one path for each OR condition. Alternatively, split your Zap into multiple Zaps, each with its own filter condition. Complex nested logic is a common source of filter errors and is much easier to debug when separated into discrete Zaps. Step 6: Add a test record in the trigger app to verify the filter end-to-end. After fixing the filter, create a real test record in the trigger app that should pass the filter (e.g., a new CRM contact with the status that your filter allows). Watch zapier.com/app/history in real time — the task should appear within 1–15 minutes depending on your Zap's polling interval. Then create a record that should be blocked by the filter and confirm no task appears in history for it. This end-to-end test is the only reliable confirmation that the filter is working correctly in production.