whether the LanguageTool Proofreading API has a form of Premium version

When using the public API to detect, it is suggested that “"You might be missing errors only the Premium version can find. Contact us at supportlanguagetoolplus.com.” Therefore, I would like to confirm with you whether the LanguageTool Proofreading API has a form of Premium version and how its charges .
Also, how can we test LanguageTool Proofreading API of Premium versione?

Please contact support .at. languagetoolplus.com for more information about the premium API access.