> For the complete documentation index, see [llms.txt](https://docs.coupler.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.coupler.io/sources/category/finance-and-accounting/coinmarketcap/common-issues.md).

# Common Issues

## Connection issues

<details>

<summary>My API key is rejected during setup</summary>

Double-check that you copied the full API key from the CoinMarketCap Developer Portal without any leading or trailing spaces. Keys are long strings — partial copies are a common mistake.

Also confirm the key is active. Log into your CoinMarketCap developer account and check that your API key status shows as **Active**, not disabled or pending.

</details>

<details>

<summary>The data flow connects but returns no data</summary>

This usually happens when the Quotes entity is selected but no symbols are entered. The Quotes entity requires at least one ticker symbol (e.g., BTC) to return data. Go back to your source settings and add symbols under the **Cryptocurrency symbols** field.

</details>

## Missing data

<details>

<summary>Historical data is empty or unavailable</summary>

Historical OHLCV data requires a paid CoinMarketCap API plan. If you're on the free Basic tier, set the **Data type** to **latest** — historical will always return empty results on a free key.

{% hint style="warning" %}
Upgrade your CoinMarketCap plan before switching to historical data type, or your data flow will consistently return no rows.
{% endhint %}

</details>

<details>

<summary>Some coins I entered are missing from Quotes results</summary>

CoinMarketCap's API rejects symbols it doesn't recognize — and it won't return partial results. Check each symbol against the CoinMarketCap website to confirm the exact ticker. Some tokens share similar names but have different official symbols (e.g., LUNA vs LUNC).

</details>

## Permission errors

<details>

<summary>I'm getting a 401 or "API key missing" error</summary>

This means Coupler.io cannot authenticate with CoinMarketCap. Re-enter your API key in the source settings. If the problem persists, regenerate your key in the CoinMarketCap Developer Portal and update it in Coupler.io.

</details>

<details>

<summary>I'm getting a 403 "access forbidden" error on a specific endpoint</summary>

Certain entities or data types (especially historical) are restricted to higher-tier API plans. A 403 error means your current plan doesn't include access to that endpoint. Review your plan permissions on the CoinMarketCap Developer Portal.

</details>

## Data discrepancies

<details>

<summary>Prices in Coupler.io don't match what I see on the CoinMarketCap website</summary>

CoinMarketCap prices update frequently. If you're comparing data pulled a few minutes ago to the live website, you'll see differences. The **last\_updated** field in your data shows exactly when the snapshot was taken — use this to verify freshness.

</details>

<details>

<summary>Market cap or volume numbers look different from other sources</summary>

CoinMarketCap uses its own methodology for calculating market cap (circulating supply × price) and aggregating volume. Other platforms may use different supply figures or volume weighting. These differences are expected — they're not a sync error.

</details>

## Rate limits

<details>

<summary>My data flow fails with a rate limit or 429 error</summary>

The free CoinMarketCap API plan has a monthly call credit limit. Each sync run consumes credits — more entities and larger datasets use more credits. Reduce your sync frequency or narrow your symbol list to stay within limits. Upgrading your CoinMarketCap plan will increase your credit allowance.

{% hint style="danger" %}
Running multiple data flows pulling the same CoinMarketCap entity simultaneously will exhaust your monthly credits faster. Consolidate entities into a single data flow where possible.
{% endhint %}

</details>


---

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