n8n-io/n8n · warning · UserError

Additional Model Request Fields must be a JSON object

Error message

Additional Model Request Fields must be a JSON object

What it means

Companion to error 682: thrown after jsonParse succeeds but isJsonObject(parsed) is false. The Bedrock InvokeModel API requires additionalModelRequestFields to be a JSON object (key/value pairs); a JSON array, number, string, or boolean is syntactically valid JSON but semantically wrong, so the UserError pinpoints the shape problem.

Source

Thrown at packages/@n8n/nodes-langchain/nodes/embeddings/EmbeddingsAwsBedrock/EmbeddingsAwsBedrock.node.ts:161

			credentials,
			bedrockRuntimeEndpoint,
			maxRetries: options.maxRetries,
			timeout: options.timeout,
		});

		let additionalModelRequestFields: Record<string, unknown> | undefined;
		const additionalFields = options.additionalModelRequestFields?.trim();
		if (additionalFields && additionalFields !== '{}') {
			let parsed: unknown;
			try {
				parsed = jsonParse(additionalFields);
			} catch {
				throw new UserError('Additional Model Request Fields must be valid JSON', {
					level: 'warning',
				});
			}
			if (!isJsonObject(parsed)) {
				throw new UserError('Additional Model Request Fields must be a JSON object', {
					level: 'warning',
				});
			}
			additionalModelRequestFields = parsed;
		}

		const embeddings = new BedrockInvokeModelEmbeddings({
			client,
			model: modelName,
			additionalModelRequestFields,
		});

		return {
			response: logWrapper(embeddings, this),
		};
	}
}

View on GitHub (pinned to 5ac6606e81)

Solutions

Wrap the value in an object: pass {"key": "value"} rather than a bare array or primitive.
If you only intended one override, find the correct parameter name in the Bedrock model docs and use it as a key.
Leave the field empty (or {}) when no additional fields are required.

Example fix

// before
options.additionalModelRequestFields = "[512, 1024]"
// after
options.additionalModelRequestFields = "{\"dimensions\": 512}"

Defensive patterns

Strategy: type-guard

Validate before calling

const parsed = JSON.parse(raw);
if (typeof parsed !== 'object' || parsed === null || Array.isArray(parsed)) {
  throw new Error('Additional Model Request Fields must be a JSON object');
}

Type guard

const isJsonObject = (v: unknown): v is Record<string, unknown> =>
  typeof v === 'object' && v !== null && !Array.isArray(v);

Try / catch

// Validate shape after parsing; reject non-objects before they reach the node.

Prevention

Always wrap overrides in an object literal: {"key": value}.
Document with examples in the node's option description.
Add a CI check that scans for additionalModelRequestFields values that are arrays/primitives.

When it happens

Trigger: User enters [1,2,3], 256, true, or "hello" in 'Additional Model Request Fields' — parses cleanly as JSON but is not an object. Also triggered by a templated expression returning a JSON array literal.

Common situations: Confusing the field with a list-style option; pasting an array of model IDs instead of request overrides; templating that emits a primitive.

Related errors

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/0a8c4ea2d1c3fa70. Report an issue: GitHub.