Click on setup and open the developer console.

In Salesforce, add an Apex Class and create an “@invocable method” (The action reads the invocable methods). Like we have created a Class “CampaignController” and added an Invocablemethod “SendCampaign” with a List of emails as a parameter(InvocableMethod only allows List<T>).
public class CampaignController {
@invocablemethod(Label='Send survey' description='Makes API call')
public static void sendCampaign(List<String> email){
String contactEmail = email[0];
if(!System.isFuture() && !System.isBatch()){
GetSurveyLinkCallout.getSurveyLink(contactEmail);
}
}
}

Inside the method, we take the Email as a parameter and call another method. In the above screenshot, you can see we have called the “getSurveyLink” method defined in the “GetSurveyLinkCallout” class.

Now create a new Class that contains your API callout. As mentioned above we have created a class “GetSurveyLinkCallout”, inside the class, we have added a method “getSurveyLink”. We have made the method “@future(callout=true)” as we have to make an HTTP call. In this method, we are updating two custom fields of contacts “Survey Link” and “Survey Link Updated” to “True”.
public class GetSurveyLinkCallout {
@future(callout=true)
public static void getSurveyLink(String contactEmail){
String apiUrl = 'https://open-api.surveysensum.com/api/v2/Share/shareSurvey/link?surveyGuid=c9341fa9-8e3e-4ccc-906f-2a268dab977e';
System.debug(contactEmail);
Http h = new Http();
httpRequest request = new HttpRequest();
request.setMethod('POST');
request.setTimeout(60000);
request.setEndpoint(apiUrl);
String authorizationHeader = 'Bearer eyJhbGciOiJSUzI1NiIsImtpZCI6ImEyNTYwZTZmMmYyMjU1NGIzOWM3NTllNGFiOWVmYWIwIiwidHlwIjoiSldUIn0.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.2YpckkxBhUJF612GxNQ6h5NS6IPeH2z7hDTfbl8elDaX3dfdkg1l4gDWPwv0C_7kXyggixE1vf-VMr_VftcE8VBbguz8NDLW5g5JZp_cJ4acC7pmU3vaaJQ1fSXYWipvDLtXWo1tGijAoK3cKHr6mRum-SWZlNmtIwomiwmuOeuLQA0OFvCHHOnDLJu2piuxtNUZXnQkTpeey1q9VLMKr1yCDofOLJWXUIxCs6rrvF4hm0AnRd1zZtDDHFt2zS8bRlJ1YP-IYQOLgo03Pu3QbJGn9tizWfHqxsDWVL-3ZbbddhYCnpsfF_i8m9AkZMJzEQkmwJcXd8muQaA4dwHUuQ';
request.setHeader('Authorization', authorizationHeader);
String requestBody = '{"contactInfo": [{"key": "vz_c_name","value": "Aashish"},{"key": "vz_c_email","value": "'+ contactEmail +'"}],"metadata": [{"key": "vz_transaction_id","value": "T-4"}]}';
System.debug(requestBody);
request.setHeader('Content-Type', 'application/json;charset=UTF-8');
request.setBody(requestbody);
HttpResponse response = h.send(request);
String respData = response.getBody();
system.debug('Response ' + respData);
if (response.getStatusCode() == 200)
{
Map<String, Object> results = (Map<String, Object>) JSON.deserializeUntyped(response.getBody());
List<Object> surveyLinks = (List<Object>) results.get('result');
System.debug(String.valueof(surveyLinks[0]));
Contact contactInstance = new Contact();
contactInstance = [SELECT Survey_Link__c, Survey_Link_Updated__c From Contact WHERE Email = :contactEmail LIMIT 1];
contactInstance.Survey_Link__c = String.valueof(surveyLinks[0]);
contactInstance.Survey_Link_Updated__c = 'True';
update contactInstance;
}
}
}