Why I can't go on dynamic services from mashup?

[fmanniti]

In my mashup I want to add a dynamic service of a thing template but I get this sign on my cursor when try to check the Dynamic box; what does it mean?

[PaiChung]

Most likely you clicked + on the black bar in the builder for an entity that already has a service mapped in that is not dynamic

use the green and white plus at the top to add a new entity.

select it and dynamic should be available.