How to encrypt a plaintext SQLite database to use SQLCipher (and avoid “file is encrypted or is not a database” errors)

SQLCipher SQLCipher FAQ
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How can this be done in C? Everytime I run

sqlite3_prepare_v2(db_plaintext, “ATTACH DATABASE ‘encrypted.db’ AS encrypted KEY ‘testkey’”, -1, 0, 0);
application crashes