Emby webhook gives certificate error

[jwstekelenburg]

Emby webhook gives the following error:

MediaBrowser.Model.Net.HttpException: MediaBrowser.Model.Net.HttpException: The SSL connection could not be established, see inner exception.
—> System.Net.Http.HttpRequestException: The SSL connection could not be established, see inner exception.
—> System.Security.Authentication.AuthenticationException: The remote certificate is invalid because of errors in the certificate chain: PartialChain

Any suggestions why?

Thanks