Validation on IOS.
If you think your project needs to validate purchases additioanly (base purchse responce validation is already performed on plugin side) you can adde server side validation to your project.
Eatch platfrom has own validation approatch, explore the guidelines bellow to find out how to perform validation for eatch platfrom.
Tell us if transaction isn't valid
In case the validation is failed, please remove purchase record from a plugin, in order to avoid a conflict. Code snippet bellow.