Error message
Deprecated function: Creation of dynamic property Drupal\mailjet_subscription\Form\SubscriptionSignupPageForm::$entity_id is deprecated in Drupal\mailjet_subscription\Form\SubscriptionSignupPageForm->setSignupID() (line 46 of modules/contrib/mailjet/modules/mailjet_subscription/src/Form/SubscriptionSignupPageForm.php).Warning: Undefined property: Drupal\mailjet_subscription\Entity\SubscriptionForm::$email_label in Drupal\mailjet_subscription\Form\SubscriptionSignupPageForm->buildForm() (line 100 of modules/contrib/mailjet/modules/mailjet_subscription/src/Form/SubscriptionSignupPageForm.php).
Deprecated function: explode(): Passing null to parameter #2 ($string) of type string is deprecated in Drupal\mailjet_subscription\Form\SubscriptionSignupPageForm->buildForm() (line 110 of modules/contrib/mailjet/modules/mailjet_subscription/src/Form/SubscriptionSignupPageForm.php).
Deprecated function: explode(): Passing null to parameter #2 ($string) of type string is deprecated in Drupal\mailjet_subscription\Form\SubscriptionSignupPageForm->buildForm() (line 111 of modules/contrib/mailjet/modules/mailjet_subscription/src/Form/SubscriptionSignupPageForm.php).
Warning: Undefined property: Drupal\mailjet_subscription\Entity\SubscriptionForm::$labels_fields in Drupal\mailjet_subscription\Form\SubscriptionSignupPageForm->buildForm() (line 112 of modules/contrib/mailjet/modules/mailjet_subscription/src/Form/SubscriptionSignupPageForm.php).
Deprecated function: explode(): Passing null to parameter #2 ($string) of type string is deprecated in Drupal\mailjet_subscription\Form\SubscriptionSignupPageForm->buildForm() (line 112 of modules/contrib/mailjet/modules/mailjet_subscription/src/Form/SubscriptionSignupPageForm.php).