Make sure that pre-order is enabled and status is displayed for the product / variant in the app. If the app displays other status then pre-ordering is not available because of some conditions: - Pre-order limit reached (configure in the product / variant settings) - Current date doesn't match pre-order schedule (configure in the product / variant settings) - There are still several items in stock.
The pre-order button is displayed only if the quantity of items in stock is less than or equal to zero.
Check that pre-order is enabled for your location. Pre-order is enabled for all countries by default. Settings→ App Settings → Overall settings → Pre-order is enabled for following locations:
Open the product page or reload already opened page with clearing cache (Ctrl+F5) and select the variant. If the pre-order button is not displayed for this variant, although the app shows status, then you should contact support.