BuildStore works properly in Safari Non-Private browsing mode only. Opening links in Private mode may cause registration loops (when it takes you back to the payment page) and other technical issues. A window that's using Private Browsing has a dark Smart Search field with white text. Also, the white highlight around the word “Private” at the bottom left corner means it is turned on.
Here's step-by-step guide how to leave Private mode:
Open Safari and tap icon at the bottom right corner.
Tap Private (lower left corner) to turn private browsing off and any Safari windows open in Non-Private Browsing mode will appear.
Tap Done and open builds.io