Sometime the invite e-mail is overlooked or it may have ended up in your spam box.
You can always go to https://pmv2.pledgemaster.games and enter the e-mail address that you use for your Kickstarter account. It is very important that you use the same e-mail as your Kickstarter account. If you do not, it will create a new account that does not have any of the funds you may have paid in through Kickstarter.
Once you have entered your e-mail you will be prompted to create a password. If you have already used Pledgemaster in the past you will be prompted to enter the password you previously created. Once you are logged in you should be able to see all of our Kickstarter campaigns you have pledged too, and any of our Kickstarter campaigns that are available for late backing.