TaxCloud vs Zamp

TaxCloud

A 30-operation REST API with a public OpenAPI 3.1 contract, llms.txt, Markdown docs and a 30-day trial that needs no card. The vendor publishes no rate limit numbers, no SLA, no API changelog and no official v3 client library, and the security page names no audit or certification.

Zamp

A free 30-day sandbox key needs no card or sales call, and the docs are served as Markdown with llms.txt and a published limit of 1,000 requests a minute. There is no OpenAPI file, SDK, API changelog or published price, production keys come with a sales-led account, and the site footer says SOC 2 compliance is in progress.

TaxCloud

1. Send X-API-KEY on every call and put the connection ID in the path, as in /tax/connections/{connectionId}/carts. A wrong ID returns 404
2. Mark nexus states active in the account first. With none active the API returns zero tax and no error
3. Use a separate test connection. There is no sandbox, and orders on a live connection go into filing
4. Pass a stable idempotencyKey on refunds, and never convert the same cart twice. A second conversion creates a duplicate liability
5. Void a wrong order before 12:00 AM Eastern on the 10th of the month after its completedDate. Later requests return 422

Zamp

1. Call POST /calculations for a quote and POST /transactions only when the sale is final. Put the returned taxDue in taxCollected when posting
2. Keep transaction and line item ids to 25 characters. A repeated POST /transactions with an existing id returns 409 CONFLICT, so a retry doesn't create a second record
3. For a refund, post a new transaction with parentId set to the sale's id and a negative quantity. Never send a negative amount on a line item
4. Send shipToAddress.state and country set to CA for Canadian orders. POST /addresses validates US addresses only
5. Page lists with limit (1 to 100, default 10) and cursor until nextCursor is null. GET /transactions returns only transactions written with the same key
6. Don't store sensitive or personal data in the sandbox. Trial data is deleted after 30 days and the trial terms forbid live customer data