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I'm using the Webhooks addon from Gravity Forms (https://docs.gravityforms.com/category/add-ons-gravity-forms/webhooks-add-on/)
to submit a form to an internal handler so I can take action on the form data.

Internally, it uses wp_remote_request() to send a request to /wp-admin/admin-ajax.php?action=application_submitted, but the
callback function never fires.

When I visit https://mysite.local/wp-admin/admin-ajax.php?action=application_submitted in my browser, 
or use curl to GET or POST to it via curl, the function works and replies 'done' to let me know.

When the webhooks plugin sends a request (either GET or POST) to the same URL, admin-ajax.php never gets run, even though I
can see with Xdebug that the correct callback has been registered to the correct hooks.

Also, when I trace out the call stack I can see that the request succeeds with 200, but never hits the breakpoint I've set on
the callback like it does with a regular page visit.

<?php
add_action( 'wp_ajax_nopriv_application_submitted', __NAMESPACE__ . '\\do_the_thing' );
add_action( 'wp_ajax_application_submitted', __NAMESPACE__ . '\\do_the_thing' );

function do_the_thing() {
	// The thing to do, but never gets done.
  
  wp_send_json( 'done' );
}

{
	"0": {
		"title": "Test GET",
		"description": "",
		"labelPlacement": "top_label",
		"descriptionPlacement": "below",
		"button": {
			"type": "text",
			"text": "Submit",
			"imageUrl": ""
		},
		"fields": [{
			"type": "checkbox",
			"id": 1,
			"label": "Does this work?",
			"adminLabel": "",
			"isRequired": false,
			"size": "medium",
			"errorMessage": "",
			"visibility": "visible",
			"choices": [{
				"text": "It works!",
				"value": "It works!",
				"isSelected": false,
				"price": ""
			}],
			"inputs": [{
				"id": "1.1",
				"label": "It works!",
				"name": ""
			}],
			"formId": 2,
			"description": "",
			"allowsPrepopulate": false,
			"inputMask": false,
			"inputMaskValue": "",
			"inputType": "",
			"labelPlacement": "",
			"descriptionPlacement": "",
			"subLabelPlacement": "",
			"placeholder": "",
			"cssClass": "",
			"inputName": "",
			"noDuplicates": false,
			"defaultValue": "",
			"conditionalLogic": "",
			"productField": "",
			"enableSelectAll": "",
			"enablePrice": "",
			"displayOnly": "",
			"multipleFiles": false,
			"maxFiles": "",
			"calculationFormula": "",
			"calculationRounding": "",
			"enableCalculation": "",
			"disableQuantity": false,
			"displayAllCategories": false,
			"useRichTextEditor": false
		}],
		"version": "2.3.2",
		"id": 2,
		"useCurrentUserAsAuthor": true,
		"postContentTemplateEnabled": false,
		"postTitleTemplateEnabled": false,
		"postTitleTemplate": "",
		"postContentTemplate": "",
		"lastPageButton": null,
		"pagination": null,
		"firstPageCssClass": null,
		"subLabelPlacement": "below",
		"cssClass": "braums-careers-application",
		"enableHoneypot": false,
		"enableAnimation": false,
		"save": {
			"enabled": false,
			"button": {
				"type": "link",
				"text": "Save and Continue Later"
			}
		},
		"limitEntries": false,
		"limitEntriesCount": "",
		"limitEntriesPeriod": "",
		"limitEntriesMessage": "",
		"scheduleForm": false,
		"scheduleStart": "",
		"scheduleStartHour": "",
		"scheduleStartMinute": "",
		"scheduleStartAmpm": "",
		"scheduleEnd": "",
		"scheduleEndHour": "",
		"scheduleEndMinute": "",
		"scheduleEndAmpm": "",
		"schedulePendingMessage": "",
		"scheduleMessage": "",
		"requireLogin": false,
		"requireLoginMessage": "",
		"confirmations": [{
			"id": "5b196c5c0011a",
			"name": "Default Confirmation",
			"isDefault": true,
			"type": "message",
			"message": "Thanks for contacting us! We will get in touch with you shortly.",
			"url": "",
			"pageId": "",
			"queryString": ""
		}],
		"notifications": [{
			"id": "5b196c5bf3f45",
			"to": "{admin_email}",
			"name": "Admin Notification",
			"event": "form_submission",
			"toType": "email",
			"subject": "New submission from {form_title}",
			"message": "{all_fields}",
			"isActive": false
		}]
	},
	"version": "2.3.2"
}