That's a tricky issue, and exchanges don't let us know the exact reasons.
Here are things to check.
Don't use IP whitelisting. 3Commas doesn't support it. Some exchanges call this: "IP restricted access", "IP binding", or "IP whitelist".
Check all required permissions. Usually, it's everything except withdrawals. Never enable withdrawal access on your 3Commas API keys. Check guides here (click the link and search using the exchange name you want to connect).
Ensure that 3Commas supports the exchange. Hint for Huobi users: only Huobi Global is available at the moment. Here's a list of supported exchanges and features.
Disable any website translation tools you have enabled in your browser, these can interfere with the display or copy and pasting of API keys.
Check if you copy anything else, such as "whitespace" before or after the API key or Secret you want to copy; for example, Android and Apple devices can sometimes add a space " " after items you copy and paste. If you are unsure, you can paste any keys to a text editor, then compare what has been pasted to the web page on the exchange showing the API Key and Secret phrases.
If you have deleted an API created earlier, please create a new one and wait 5 minutes before adding it to 3Commas.
Unfortunately, we cannot see or check the API permissions you created on the exchange account.
When you think everything is OK, go to the My Exchanges page and click the refresh button by the exchange you just added or updated; if this works without an error, then try a test by performing Smart Trade with a small amount of funds.
If the smart trade fails then this usually indicates an issue with the API permissions set on the exchange.
If you faced another error about API, take a look here: