Encoding argument $3 failed: attempted to encode a non-document type at the top level: Array

Signing up doesn't seem to work on `sqlx-sqlite`; it always seems to give this weird error?
```rust
[backend/src/api/register.rs:6:5] auth.signup(&form).await = Err(
    SqlxError(
        Encode(
            "Encoding argument $3 failed: attempted to encode a non-document type at the top level: Array",
        ),
    ),
)
```

Am I doing something wrong?