Please make sure your unit number and postal code is CORRECT. You will bear the cost for the second postage if your mail bounces!
E.g.:
1) PTV > Slam Dunk Fest 2013 > 1st page, 6th photo
Size: 11 x 14
US$15
2) OM&M > Warped Tour 2013 > 3rd page, 10th photo
Size: 8 x 10
US$10
E.g. You might be out of the country or going for some camp, and you think it might clash with the date of second payment or anything.