ERR_PAYLOAD_TOO_LARGE on Zapier: Payload too large. Root cause: The HTTP request body exceeds the maximum payload size enforced by the API endpoint. This commonly occurs when sending large file attachments, bulk record arrays, or rich text fields with embedded base64-encoded images in a single API call. Step 1: Identify what is in the payload. In Zapier task history, expand the failing step and look at the "Request Body" section. Identify whether the large data is a file attachment (base64-encoded), a long text field, or a large array of records. The Zapier payload limit is 10MB for most actions. Step 2: Remove base64-encoded file content from the payload. If you are passing file content directly in the request body (e.g. a base64-encoded PDF or image), this is the most common cause. Instead, upload the file to a storage service (Google Drive, Dropbox, S3) first, then pass only the file URL in the Zapier action. The receiving API can fetch the file from the URL. Step 3: Truncate or summarise long text fields. If the payload is large because of a long text field (e.g. email body, notes, description), add a Zapier Formatter step before the failing action. Use the "Truncate" transform to limit the field to a safe length — typically 5,000 characters is sufficient for most CRM and helpdesk APIs. Step 4: Split bulk record arrays into batches. If the payload contains an array of records (e.g. sending 50 contacts at once), split it into smaller batches. Use Zapier's Looping by Zapier app to iterate over the array and send one batch of 10 records per loop iteration. Step 5: Verify the target API's own size limit. Different APIs have different maximum payload sizes. Check the documentation for the target API (e.g. HubSpot, Salesforce, Slack) to confirm their specific limit. Some APIs have limits as low as 1MB. If your payload is within Zapier's limit but the target API rejects it, the target API's limit is lower.