Preview writes nothing. Sync is safe to re-run.
Preview computes the full answer for a product and changes nothing at your billing system or at the vendor. It asks that product's own server entry which regions its reseller account currently serves, checks each region's certificate, and shows you the result. Always run this first, especially the first time you configure a product.
Sync performs the same check and then writes the resulting option group into your product catalogue. It reports six change counts, and running it a second time with nothing changed reports zero for all six — that is what makes it safe to click again later, for example after adding a new region. A region that stops being offered is hidden rather than deleted, so a customer who already bought it keeps a service that still resolves to what they originally chose.
Neither button is a link. Both submit a form, so neither can be triggered by loading a URL by itself.
The region allow-list is a ceiling, never an authority
The Region Allow-list on the Settings view is install-wide and only ever narrows what is offered — it can never grant a region your reseller account doesn't itself serve. Leaving it blank is the correct choice for most installs: it means every region your account reports is offered. If you do name a region your account does not serve, it is reported back to you rather than silently dropped.
A region is only actually offered to customers once three things are true: your account serves it, its endpoint's certificate verifies, and the vendor reports it as currently accepting new storage. A certificate proves a name resolves; it says nothing about whether the vendor will accept a new account there.
If Sync refuses
Every refusal is reported by name and writes nothing at all. The refusal is always shown together with the full region table underneath it, listing each region's code, whether it is orderable, and if not, exactly what excluded it — that table is the answer to "why is the region I expected missing." The most common causes are a product left on server group zero, a server group holding more than one entry of this module's type, or Storage Tiers still blank.
Storage Tiers have no quota field
Each tier you define is a name and a label — key|Label — and nothing else. There is no third field for a size or a price. This is why the overage policy's automatic-upgrade option is not offered anywhere in this module: there is no quota value anywhere for it to read as a target.