Speech Central doesn’t provide any distribution, sales, payment processing, licensing and related services to end-consumers. Those services are provided by other companies that take the fee from the user payment to provide such a service (like Apple App Store, Google Play, Microsoft Store). You need to contact their support for related questions. If you have purchased the app their contact should be available in their e-mail receipt.
The licenses issued by those companies cannot be activated on another company’s service or even on another platform (like between iOS and macOS)1. This is clearly indicated in the app’s description on the store.
It is a general policy of those companies to allow license to be used on multiple devices that run the same operating system under the same user account. Each provider allows limited number of devices and the limit may change over the time. For the information on the exact number you need to contact your licensing provider. If the license is in the form of in-app purchase you may need to manually activate it on the new device by going to Extras > Restore Purchases.
While this may require some users to buy multiple licenses for multiple platforms, the overall pricing strategy is accommodated to that. As this strategy allows Speech Central to avoid running its own licensing servers and monthly cost related to that, Speech Central doesn’t have to charge monthly subscription like some other apps do. As such, it is up to 100x less expensive than competing apps with similar feature set when used in the long term.
All users that use VoiceOver or Talkback assistive technologies have in-app purchases (licenses on iOS and Android) activated for free by default.
Note:
1 Apple allows license sharing among iOS and macOS apps for new apps launched after 2020. Speech Central was launched before that and to participate in license sharing it would need to discard the macOS app and leave all legacy users without updates. Further to keep the app sustainable the common license would cost 50% more – that would benefit some users that would save some money but it would also make the app cost more for other users.