Plan requirement
| App | pluscloud AI Agent Preview |
| Subscription | Suite Team or higher, Support Team or higher |
| Access | Client admin, Client editor, Client user |
The limits the preview checks per channel, with the source of each number. A message above a limit is marked as not delivered or as probably not delivered.
How to read this table
Not delivered means the source states that such a message is rejected. Probably means the limit is documented, but what happens above it is not. Where Zendesk or Sunshine Conversations publishes a limit, that source comes first; for numbers Zendesk does not publish, the source is the documentation of the channel itself. What you do about a marked message is in Messages marked as not delivered.
The limits were checked against these sources on 4 October 2026. Channels change their limits from time to time, so check the source before you rely on a number.
Every messaging channel
| The preview marks a message when | Marked | Source |
|---|---|---|
| The text is longer than 4,096 characters | Not delivered | Sunshine Conversations API reference, Zendesk: What is the character limit for messaging? |
| A carousel has more than 10 cards, more than 3 buttons on a card, or a card title or description longer than 128 characters | Not delivered | Zendesk: Using carousels in conversation flows for AI agents |
This applies to the Web Widget and the Zendesk SDKs as well. A channel's own text limit above 4,096 characters never comes into play, because Sunshine Conversations rejects longer text first. That is why the table below has no text limit for LINE, Viber or X.
Per channel
| Channel | The preview marks a message when | Marked | Source |
|---|---|---|---|
| A reply button is longer than 20 characters | Probably | Zendesk: customer message block, Meta: reply buttons | |
| Two reply buttons have the same label | Not delivered | Sunshine Conversations: WhatsApp, Meta: reply buttons | |
| The text is longer than 4,096 characters, or a generative reply comes within 200 characters of it, because the AI disclaimer is added to the text | Probably | Meta: text messages, Sunshine Conversations API reference | |
| The text of a message with reply buttons is longer than 1,024 characters | Probably | Meta: reply buttons | |
| An image caption is longer than 1,024 characters | Probably | Meta: image messages | |
| A list option is longer than 24 characters | Probably | Meta: list messages | |
| Messenger | The text is longer than 2,000 characters | Not delivered | Zendesk: Adding Facebook Messenger channels |
| Messenger | The text of a message with buttons is longer than 640 characters | Probably | Meta: button template |
| The text is larger than 1,000 bytes; emoji and accented letters take more than one byte each | Probably | Meta: Instagram messaging | |
| Telegram | The text is longer than 4,096 characters, or a photo caption longer than 1,024 | Probably | Telegram Bot API |
| LINE | The text of a message with buttons is longer than 160 characters. LINE allows 60 when the message also has an image or a title; the preview checks the 160. | Probably | LINE Messaging API: buttons template |
| Viber | The sender name, which is the AI agent's display name, is longer than 28 characters | Not delivered | Sunshine Conversations: Viber, Viber REST Bot API |
| Viber | A picture caption is longer than 768 characters | Probably | Viber REST Bot API |
| RCS | The text is longer than 3,072 characters, there are more than 11 suggestions, or a suggestion is longer than 25 characters | Probably | Google: RCS Business Messaging |
| SMS | The text, including the options added to it as text, is longer than 1,600 characters | Not delivered | Twilio: error 21617 |
| Slack | A text block is longer than 3,000 characters, or a button label longer than 75 | Probably | Slack: section block, Slack: button element |
| Nothing is checked |
For WhatsApp, the legacy AI agents had a limit of 4,095 characters and cut longer text off; Zendesk describes that in Is there a character limit for AI agent messages in WhatsApp.
Turn the check off
In Preview settings, turn off Simulate channel limits. See The preview settings.
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