property 'subscribe' does not exist on type '() = observable

Makes sure you have used observable type return method.

For more reference visit these are the sites,

https://angular.io/guide/observables

https://stackoverflow.com/questions/44092034/property-subscribe-does-not-exist-on-type-observableany

https://forum.ionicframework.com/t/ts-property-subscribe-does-not-exist-on-type-res-any-any/112627