Update README.md

README.md

@@ -16,6 +16,10 @@ The core of the integration is provied by [plugp100](https://github.com/petretia
 [![License][license-shield]](LICENSE)
 [![BuyMeCoffee][buymecoffeebadge]][buymecoffee]
 
+## Warning!!!
+For some unknown reason email with capital letter thrown an "Invalid authentication" error. So before open an new issue check your email address on Tapo App Settings. If contains capital letter, the integration won't work. I've opened an issue that explain this [#122](https://github.com/petretiandrea/home-assistant-tapo-p100/issues/122), I will fix asap. As workaround you can create a new account using all lower-case in your email address.
+
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 ## Features
 
 - [x] pure async home assistant's method