Error while sending pushes through mobile

Your software
My Mautic version is: 3.2.1
My PHP version is: 7.4
My Database type and version is: mysql 7.4

Your problem
I am trying to send pushes through Mautic to my mobile. In the docs it states to make an entry using

/notification/appcallback

I am getting

{
“contact_id”: “4187”,
“stat_recorded”: false,
“push_id_recorded”: true
}

and a contact is getting created. But when I try to send push to that contact, it gives me an error

This event encountered an error during the last attempt to process

These errors are showing in the log:

`

mautic.NOTICE: PHP Notice - Trying to access array offset on value of type null - in file /var/www/html/mautic/app/bundles/NotificationBundle/Form/Type/MobileNotificationSendType.php - at line 80 {“builder”:"[object] (Ivory\OrderedForm\Builder\OrderedFormBuilder: {})",“options”:{“block_name”:null,“disabled”:false,“label_format”:null,“translation_domain”:null,“auto_initialize”:true,“trim”:true,“required”:true,“property_path”:null,“mapped”:true,“by_reference”:true,“inherit_data”:false,“compound”:true,“method”:“POST”,“action”:"",“post_max_size_message”:“The uploaded file was too large. Please try to upload a smaller file.”,“allow_file_upload”:false,“error_mapping”:,“invalid_message”:“This value is not valid.”,“invalid_message_parameters”:,“allow_extra_fields”:false,“extra_fields_message”:“This form should not contain extra fields.”,“csrf_protection”:true,“csrf_field_name”:"_token",“csrf_message”:“The CSRF token is invalid. Please try to resubmit the form.”,“csrf_token_manager”:"[object] (Symfony\Component\Security\Csrf\CsrfTokenManager: {})",“csrf_token_id”:null,“label”:false,“attr”:,“data”:null,“data_class”:null,“empty_data”:"[object] (Closure: {})",“error_bubbling”:true,“label_attr”:,“upload_max_size_message”:"[object] (Closure: {})",“validation_groups”:null,“constraints”:,“position”:null,“update_select”:“campaignevent_properties_notification”},“windowUrl”:"/s/mobile_notifications/new?contentOnly=1&updateSelect=campaignevent_properties_notification"}

`