Hello @LewisS, Your speculation is correct, the format_type property used when creating an email campaign via our v3 API does control whether the campaign is created in the format used by our legacy custom code editor (format_type 1) or our modern custom code editor (format_type 5). As you noted, users of our website interface are no longer able to edit or schedule campaigns that are in the legacy format; they are only able to copy them into the modern format. This change was initially made last month, but was temporarily rolled back. It was re-implemented a few days ago. It is still possible to schedule campaigns in the legacy format using the v2 API, however the v2 API does not have the ability to create email campaigns in the modern custom code format. Our development and implementation of newer features is focused on the v3 API, as the current version. If you do need to continue with a mixed workflow (creating campaigns via the API, scheduling via the website), the best solution would be to migrate your integration to the v3 API. You are also correct that, in the modern custom code editor, square brackets are not supported within the subject line. Square brackets are reserved due their use in Subject Line Personalization, which was not available in the legacy custom code editor. While I'm unable to estimate when or if support for brackets in the subject line could be added, we do have an open feature request, and I've added your account's interest to that request. Please let us know if you have any questions.
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