Fix this before you look at anything else.
If the plugin cannot reach Mollie, nothing downstream can possibly work. Your checkout will be empty, your payments will not process, and every other troubleshooting article will send you chasing a problem you do not have.
Where you see it
Two places tell you the same thing.
The Test connection button, on the API keys tab. If the connection is broken, this comes back with “Connection failed” and a reason.
The badge at the top of the plugin. If it says Connection issue, the last attempt to reach Mollie failed. Click the badge to run a fresh check.
What a working connection looks like
When you click Test connection and everything is fine, the plugin tells you something like:
Connected! Test key works. 5 active method(s) found.
Read that second sentence, because it is more useful than it looks.
If it says 0 active methods found, your key is working perfectly. The problem is at Mollie: you have not switched any payment methods on in your Mollie dashboard. Go to Settings, then Payment methods there, and switch some on.
That single number answers a lot of support emails.
The causes, in the order they actually happen
1. The key is incomplete
By far the most common. You selected the key with your mouse and missed a character at the start or the end.
The plugin often catches this and tells you directly: The stored key looks corrupted or incomplete. Please re-enter it via Edit and save again.
The fix: go back to your Mollie dashboard, Developers, then API keys, and use the copy button next to the key. Do not select it by hand. Paste it into the plugin, save, and test again.
2. The keys are in the wrong fields
Also very common, and easy to miss.
Your test key belongs in the Test API key field, and your live key in the Live API key field. If you swap them, the plugin will faithfully try to use a test key for live payments and fail.
They start with different words, so look carefully. A live key and a test key are distinguishable at a glance once you know to look.
3. There is no key for the mode you are in
If Active mode is set to LIVE but you only ever filled in the test key, there is nothing to connect with.
The badge tells you this specifically: it will say LIVE, NO KEY.
The fix: fill in the live key, or switch back to test mode.
4. Your host is blocking outgoing connections
The plugin has to reach out to Mollie’s servers. Some hosts, particularly cheaper shared hosting, block outgoing connections by default.
You will usually see a timeout rather than a rejection: the test just sits there and then fails.
The fix: ask your hosting provider whether outgoing HTTPS requests are allowed from your website. They will know what you mean. Sometimes they need to whitelist Mollie’s domain.
This is worth ruling out early if you are on very cheap hosting, or if your site is behind a corporate firewall.
5. The key has been revoked at Mollie
If you or someone else generated a new key in the Mollie dashboard, the old one stops working immediately.
The fix: go and get the current key from Mollie, and paste it in again.
6. Mollie is having a bad day
It is rare, but it happens to everyone eventually.
How to tell: check Mollie’s status page, or simply wait ten minutes and click Test connection again. If your key has not changed and nothing on your site has changed, and it suddenly works again, that was it.
This one is not your fault and there is nothing to fix.
Still failing?
Open the System tab and click Run checks. Copy the whole report and send it to us.
The report deliberately leaves your API keys out, so it is safe to send. It tells us what your setup looks like from the inside, and it usually means we can answer you properly the first time instead of asking you to go and check six things.
While you are here
Once your connection works, click Test webhook on the same tab.
The two are different things, and both need to work. Test connection proves your website can reach Mollie. Test webhook proves Mollie can reach your website. A payment needs both journeys to succeed.
If Test webhook fails, see the article “The payment worked but nothing happened”.