PHP Fatal error Uncaught Error Call to a member function then on null in

This error message indicates that you are attempting to call the "then()" method on a null value in your PHP code. The "then()" method is typically used in conjunction with promises in asynchronous programming.

To resolve this error, you should check the code to make sure that the object you are attempting to call "then()" on is not null. You may need to add additional error handling and defensive programming to ensure that the code can handle unexpected null values.

Additionally, you should review the documentation and examples for the specific library or framework you are using to understand how to properly use promises and avoid null reference errors.