Hey, Andreas,

I assume that this is moved to https://nuget.episerver.com/en/OtherPages/Package/?packageId=EPiServer.DynamicContent.

BR,
Marija

Thanks a ton for pointing me in the right direction. And for everyone else finding this post - this is what I had to do:

In my class CustomTinyMCEButtons I added (there was already such class in the solution I'm working on)

 public const string EpiDynamicContent = "epidynamiccontent";

(In EPiServer.Editor.TinyMCE.Plugins.EPiDynamicContent from the EPiServer.DynamicContent NuGet I found the TinyMCEPluginButton with ButtonName epidynamiccontent)

And then in my DefaultTinyMCESettings class in the GetPropertySettings-method I changed 

 TinyMCEButtons.EPiServerDynamicContent,

to

 CustomTinyMCEButtons.EpiDynamicContent,

Had the same issue, verified that the constant "epidynamiccontent" dosen't exists anymore in any of the EPiServer libraries (except for descriptor and tinymcepluginbutton).