I tried the same thing, and it worked fine when trying to create an index in FRANKFURT_GERMANY
My request was:
I would suggest you double-check your API KEY, API EMAIL and the other parameters.
Also, try to use core_type=generic
Opensolr no longer supports the usual templates for indexes, since all files are editable and uploadable via the APIs, so, users can just set their own solr config-sets for their indexes.
Oherwise it should work just fine.
Can you try again and post the outcome here please?