Solving 'mismatched entity and/or field definitions' error in Drupal 8

In some cases, after installing a new module, the status report page in Drupal 8 is displaying errors such as 'Mismatched entity and/or field definitions'. Most of us might have come across this situation even though the module which caused such errors is different. I too have faced similar issue when I installed path auto module. I was getting errors in status report page as shown below:-

Mismatched entity and/or field definitions

We are getting this error because drupal 8 doesn't auto-update fields and entities upon installation of new modules. There are two ways by which you can update entities.

1) If you have drush, the following command would fix the issue:-

drush entity-updates

2) If you don't have drush, please add the following script before $response->send(); in index.php file(located in Drupal root folder) and reload the web page.

try {
\Drupal::entityDefinitionUpdateManager()->applyUpdates();
}
catch (EntityStorageException $e) {
print_r($e);
}

That's all. Now you can notice that the error message is disappeared in status report page since all entities are updated. Of course, you need to remove the above script from index.php once you fixed the error.

Hope it helps. Please contact me if you have any questions.