21728: Campaign registration failed due to length validation failures

This error appears when your US A2P 10DLC Campaign registration includes one or more fields that do not meet the documented length requirements for campaign creation. Common fields with length limits include description, messageFlow, each entry in messageSamples, and optional keyword-response fields such as optInMessage, optOutMessage, and helpMessage.

• The description value is shorter than 40 characters or longer than 4096 characters.
• The messageFlow value is shorter than 40 characters or longer than the allowed maximum for the Campaign API.
• You provided fewer than two messageSamples, more than five messageSamples, or one of the samples is shorter than 20 characters or longer than 1024 characters.
• An optional field you supplied exceeds its limit, such as optInMessage, optOutMessage, or helpMessage at 20 to 320 characters, or optInKeywords, optOutKeywords, or helpKeywords over 255 characters.
• The text you submitted is too short to satisfy the field requirements. For example, description must explain who is sending messages, who receives them, and why messages are being sent, and messageFlow must explain how end users opt in.

• Review every text field in your Campaign submission and update any value that is outside the documented length limits before you resubmit.
• Update description so it clearly explains who the sender is, who the recipients are, and why messages are being sent. Keep the value within the allowed length range.
• Update messageFlow so it fully describes every opt-in path you use. If you collect consent in more than one way, list all methods in the same field and keep the value within the documented limit.
• Provide two to five realistic messageSamples that match the selected use case. Keep each sample within the allowed length range, include the Brand name or website in each message, and use square brackets [] for variable content.
• If you manage keyword-based opt-in, opt-out, or help flows yourself, make sure the related messages and keyword lists are included when required and fit their documented length limits.
• If you are correcting a rejected Campaign in Console, update the Campaign description, sample messages, and consent details in the resubmission form, then retry review.

• A2P 10DLC - Gather the Required Business Information
• UsAppToPerson Resource
• Troubleshooting and rectifying A2P Campaigns