There are custom Interaction Types that were created using Manage Interaction Content configuration step on Manage Your Solution app. These interaction types are not going to be used anymore and you want to delete them, but can't find an option to do so.
SAP Marketing Cloud
It's not possible to delete custom interaction types.
You can suppress the usage of these unwanted custom interaction types by disabling the assignment of the interaction type and the communication medium to a channel. This is also done using the Manage Interaction Content configuration step.
You can check more details about the usage of the configuration step on the following web page: SAP Help - Managing Interaction Content
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