Weebly updated its checkout page codes on June 17 2015. This can cause the checkout page to not load due to the code change. This is an update on the no-header page layout that is used by Weebly as the checkout page.
step2: Login to your Weebly account
step3: Click into “design” then into “edit html/css”
step4: On the left hand column, you will find the “HEADER TYPE” or “LAYOUT” for older builder. Below you will find your list of page layout for your theme.
step5: Click on no-header.html page layout
step6: DELETE all codes inside no-header page
step7: Open the file downloaded in STEP 1 with NOTEPAD for PC users OR TXTEDIT for MAC users. Select & Copy ALL codes in side the document. Now PASTE the copied code in the now empty no-header.html page.
important: make sure you wait till you see the LOADING icon appear then disappear before attempting to save your change
step8: Save your changes and re-publish your site.