well the link your posting above is not our site its paypal so I really cant say much about any error you get on there. I know many users use paypal without issue.
The normal procedure for placing a paid ad is you upload the ad click the pay button it takes you to paypal you complete payment and then click the link to go back to the site.
As far as checks there is no option as stated so however you handle that is up to you.
Here is your ad
Message - PhotoPost Classifieds
Your telling me you dont see that