Creates a tier.
The name for a tier and the amount of required points to qualify for a tier can only exist for a single tier.
Attempts to create a tier with a tierDefinition.name or requiredPoints that already exists will return an error.
To create up to 20 tiers at once, use Bulk Create Tiers.
Note: You must have a Business VIP Premium plan or a Scale Premium plan to add tiers.
You can only call this method when authenticated as a Wix app or Wix user identity.