Synchronize Salesforce opportunity data with Square Peg's PMS external system|| Challenge 4

[@Salesforcebuddy1711]

ProjectCalloutService :-
public class ProjectCalloutService {
//method to be invoked by ProcessBuilder apex
@InvocableMethod
public static void postOpportunityToPMS(List oppoIds){
Opportunity opp = [SELECT Id,Name,Account.Name,CloseDate,Amount FROM Opportunity WHERE Id = :oppoIds[0]];
String serviceToken = ServiceTokens__c.getValues('ProjectServiceToken').Token__c;

String jsonInput = '{
' +
' "opportunityId" : "'+opp.Id+'",
'+
' "opportunityName" : "'+opp.Name+'",
'+
' "accountName" : "'+opp.Account.Name+'",
'+
' "closeDate" : "'+String.ValueOf(opp.CloseDate).mid(0,10)+'",
'+
' "amount" : "'+opp.Amount+'"
}';

System.enqueueJob(new QueueablePMSCall(serviceToken, jsonInput, opp.Id));
}

class QueueablePMSCall implements System.Queueable, Database.AllowsCallouts{
private String serviceToken;
private String jsonInput;
private Id oppId;

public QueueablePMSCall(String serviceToken, String jsonInput, Id oppId){
this.serviceToken = serviceToken;
this.jsonInput = jsonInput;
this.oppId = oppId;
}

public void execute(QueueableContext qc){
postToPMS(serviceToken, jsonInput, oppId);
}
}

@Future(callout=true)
private static void postToPMS(String serviceToken, String jsonInput, Id oppoId){
HTTPRequest req = new HTTPRequest();
req.setEndPoint('callout:ProjectService');
req.setMethod('POST');
req.setHeader('token',serviceToken);
req.setHeader('Content-Type', 'application/json;charset=UTF-8');
req.setBody(jsonInput);

HTTP http = new HTTP();
HTTPResponse res = http.send(req);

Opportunity opp = new Opportunity(Id=oppoId);
if(res.getStatusCode() == 201){
opp.StageName = 'Submitted Project';
System.debug('Success: ' + res.getStatus());
}else{
opp.StageName = 'Resubmit Project';
System.debug('Failure: ' + res.getStatusCode() + ' ' + res.getStatus());
}
update opp;
}
}

[@doruksonmez9218]

Changed my whole code and still same error. 500 Internal Server Error

[@amitjodha]

I too am facing this

[@subhambhattacharyya8802]

Change "class QueueablePMSCall implements System.Queueable, Database.AllowsCallouts" to "class QueueablePMSCall implements Queueable, Database.AllowsCallouts"