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I'm not a Moderator, but it might help to provide more information. At what point does it fail? I was able to go up to the PayPal login to send actual funds.
Click on a moderator's name that appears on the bottom of the title page for the forum where you need them. That will bring up their profile. Scan down their profile and find the link that says to send a Private Message (referred to as a PM) to that person. Follow the instructions that pop up with the new window.
Alternately, if you find a moderator's post in a thread, click on their username just to the left of the post itself. A menu will pop up that includes a link to click on to send them a Private Message. This method will work for sending a PM to anyone who posts in a thread and doesn't have PMs to them turned off.