You need to send an email to email@example.com
but this will immediately bounce back with a response in German as part of their anti-spam measures. In the message there is an url you have to open in a browser which will ask you to do something that a web bot won't get right. Once you do the correct thing the email will go through and in future your email sender address will be accepted.
They were very helpful and sent me replacements and gave advice on how to stick them back properly
"you have to stick with superglue.
First fill the hole with glue
Second dip the knob once or twice in the glue.
Third Place the knob into the hole and press firmly.
There must be no air under the knob."
(just minor edits to help their english translation - my german is non-existent)
Excellent support and they are great butt hooks.