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