Why do I get the error "The envelope could not be sent"

There could be multiple reasons for an error like this to show:

First; Check the API log to check for a Response Code and Reason.

Test Connection to DocuSign

In DocuSign Administration use this option:

you should receive a confirmation like this. If not, contact your system administrator.

Report used as attachment

Sometimes this happens because the report setup to serve as attachment (the one to be signed) does not create any output.

In those scenarios you will see a Response like this in the API log:

Try and run the report from the record you are trying to send to DocuSign. If you get an error like this, that is why the envelope could not be send.