If you are trying to create a fundraising page but are unable to get past completing your profile, you just need to add a full name to your account.
These are the steps to follow:
Make sure you are logged in to your JustGiving account
Click on your name/picture in the top right of your screen and select "Personal details"
Click on "Edit" next to your name and make sure you add a name in the 'First name' and 'Last name' fields
Then click on "Start fundraising" at the top of your screen and you will be able to create a fundraising page successfully