@e e 10 minutes is the maximum amount of audio length that can be produced by a request. See the limits on this page.
You will have to move to batch synthesis API to have audio files produced for more than 10 minutes if the text is too large. Also, you will have to use the standard tier of pricing to use this feature.
As a workaround, you can use your text in parts to create multiple audio files and then stich them together, but this will require some pre and post processing on the client side and you might run out of character limit under the free tier.
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