Which version of OpenCart module do I need?
The OpenCart version is put in the bottom of the page 'dashboard' in your OpenCart backend. Check always if you have the right module for the right version of OpenCart.
Refresh the OpenCart cache when you have made changed, to activate them. Go to the modifications page and select the SendCloud module. Refreshing cache is done to click on the orange and blue button.
The error is shown as follows:
'SendCloudApiException' with message 'Authentication required'. On the next line: sendcloud_api.php on line 266
This means that your API connection is not called in the right way. To fix this, check if your API keys are filled in correctly, without spacing in between (also check any spaces before or after your keys).