Just checked again, there’s no error message or really any kind message I’m able to catch except for the onClose which is throwing an error code 1006. When I switch the event kind to 1 and remove the parameterized replaceable event tags blastr accepts it.
Here is an example crosspost note that fails on blastr: note1fdvjrf6n7k659vy6zveds9qqf52eagjlq2gv2ds73ueh7rhttk7s82rud3