type: object
description: >-
You can input a merge variable payload object to your template to render
dynamic content. For example, if you have a template like:
`{{variable_name}}`, pass in `{"variable_name": "Harry"}` to render
`Harry`. `merge_variables` must be an object. Any type of value is accepted
as long as the object is valid JSON; you can use `strings`, `numbers`,
`booleans`, `arrays`, `objects`, or `null`. The max length of the object is
25,000 characters. If you call `JSON.stringify` on your object, it can be no
longer than 25,000 characters. Your variable names cannot contain any
whitespace or any of the following special characters: `!`, `"`, `#`, `%`,
`&`, `'`, `(`, `)`, `*`, `+`, `,`, `/`, `;`, `<`, `=`, `>`, `@`, `[`, `\`,
`]`, `^`, `` ` ``, `{`, `|`, `}`, `~`. More instructions can be found in [our
guide to using html and merge
variables](https://lob.com/resources/guides/general/using-html-and-merge-variables). Depending
on your [Merge Variable
strictness](https://dashboard.lob.com/#/settings/account) setting, if you
define variables in your HTML but do not pass them here, you will either
receive an error or the variable will render as an empty string.
maxLength: 25000
nullable: true