Do you use Skrill? If so, you may have received an email from them that says something like:
We are updating Skrill for Blesta 4.1 to use the new API endpoint, but if you need to use the new endpoint before you upgrade to 4.1, you can use the attached file.
This is currently a test release, so please make sure it works for you before leaving it in place.
Backup ~/components/gateways/nonmerchant/skrill/lib/skrill_api.php
Upload the attached file, overwriting the one above
Test
skrill_api.php