White screens when you try to submit, hmm; do your error logs have any new entries, specifically 503 errors? It's possible that your webhost recently installed Suhousin (probably about the same time your most recent entry into the SFS database was) and it could be killing the request... In fact, I put a lot of time into UBB.threads v7.6.0+ System Requirement Test - 20160222 because of Suhosin errors over the years.

The API key for SFS (the configuration options and a "Test" link are also on this page) are stored at:
CP -> Master Settings -> Primary Settings -> Stop Forum Spam

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