Error: MissingPluginException(No implementation found for method setApplicationId on channel square_in_app_payments)

Hi i am trying to use Square in-app payment. Right now the sandbox does not work as only real cc/debit cards navigate to the next page that displays keying in of further card details. Using iOS iPhone 12 Pro emulator When i try to initiate payment a pop comes up saying
“Something went wrong. Please contact the developer of this application and provide them with this error code: unexpected”

Then there was a time i was getting the error below:

Error: MissingPluginException(No implementation found for method setApplicationId on channel square_in_app_payments)