Implicitly convertible to `System.IDisposable'

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Hello,

I'm doing the Simple server-controlled chat of Photon Bolt https://doc.photonengine.com/en-us/bolt/current/advanced-tutorials/chat but at the line 27 the "using" give me an error:
error CS1674: `SendChatMsgToServer': type used in a using statement must be implicitly convertible to `System.IDisposable'

So is the tutorial wrong or it's me ? Can someone explain me how to solve it please.

Thanks

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