square.onMerchantCustomAttributeOwnedUpdated subscribes to merchant.custom_attribute.owned.updated for the selected seller. It requires MERCHANT_PROFILE_READ.
Example
automations/square-on-merchant-custom-attribute-owned-updated.automation.ts
Event
A custom attribute owned by your application was created or updated for a merchant. The signal resolves to the officialSquare.MerchantCustomAttributeOwnedUpdatedEvent payload with type narrowed to merchant.custom_attribute.owned.updated.