Achieving reverse workflow movement is tricky in BPM workflow. I tried such use case. I am providing potential approach for same in below write-up.
Reverse flow for sequential workflow
Reverse flow for Parallel workflow
Reverse flow can be achieved in activiti task using adding conditional links with appropriate source references.
e.g flow can be directed from Pay back to First task using conditions like
${sourceEvent == 'XXX'} etc.
flow can be directed from Xtask to approve using appropriate conditional statements.
Parallel gateway have behavior of fork and join.
So extra logic need to build to keep taking of waiting and completed tasks.
Please see attached sample BPMN and Test case to run this logic.
<?xml version="1.0" encoding="UTF-8"?>
<definitions xmlns="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:activiti="http://activiti.org/bpmn" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlns:omgdc="http://www.omg.org/spec/DD/20100524/DC" xmlns:omgdi="http://www.omg.org/spec/DD/20100524/DI" typeLanguage="http://www.w3.org/2001/XMLSchema" expressionLanguage="http://www.w3.org/1999/XPath" targetNamespace="http://www.activiti.org/test">
<process id="SampleReverse" name="SampleReverse" isExecutable="true">
<startEvent id="startevent1" name="Start"></startEvent>
<userTask id="FirstLevel" name="FirstLevel"></userTask>
<exclusiveGateway id="exclusivegateway1" name="Exclusive Gateway"></exclusiveGateway>
<sequenceFlow id="flow1" sourceRef="FirstLevel" targetRef="exclusivegateway1"></sequenceFlow>
<userTask id="SecondLevel" name="SecondLevel"></userTask>
<exclusiveGateway id="exclusivegateway2" name="Exclusive Gateway"></exclusiveGateway>
<sequenceFlow id="flow2" sourceRef="SecondLevel" targetRef="exclusivegateway2"></sequenceFlow>
<userTask id="ThirdLevel" name="ThirdLevel"></userTask>
<sequenceFlow id="flow3" sourceRef="exclusivegateway2" targetRef="ThirdLevel">
<conditionExpression xsi:type="tFormalExpression"><![CDATA[${backButton == 'false'}]]></conditionExpression>
</sequenceFlow>
<sequenceFlow id="flow4" sourceRef="exclusivegateway1" targetRef="SecondLevel"></sequenceFlow>
<sequenceFlow id="flow6" sourceRef="startevent1" targetRef="FirstLevel"></sequenceFlow>
<sequenceFlow id="flow7" sourceRef="exclusivegateway2" targetRef="FirstLevel">
<conditionExpression xsi:type="tFormalExpression"><![CDATA[${backButton == 'false'}]]></conditionExpression>
</sequenceFlow>
<exclusiveGateway id="exclusivegateway3" name="Exclusive Gateway"></exclusiveGateway>
<sequenceFlow id="flow8" sourceRef="ThirdLevel" targetRef="exclusivegateway3"></sequenceFlow>
<endEvent id="endevent1" name="End"></endEvent>
<sequenceFlow id="flow9" sourceRef="exclusivegateway3" targetRef="endevent1">
<conditionExpression xsi:type="tFormalExpression"><![CDATA[${backButton == 'false'}]]></conditionExpression>
</sequenceFlow>
<sequenceFlow id="flow10" sourceRef="exclusivegateway3" targetRef="SecondLevel">
<conditionExpression xsi:type="tFormalExpression"><![CDATA[${backButton == 'false'}]]></conditionExpression>
</sequenceFlow>
</process>
<bpmndi:BPMNDiagram id="BPMNDiagram_myProcess">
<bpmndi:BPMNPlane bpmnElement="myProcess" id="BPMNPlane_myProcess">
<bpmndi:BPMNShape bpmnElement="startevent1" id="BPMNShape_startevent1">
<omgdc:Bounds height="35.0" width="35.0" x="70.0" y="111.0"></omgdc:Bounds>
</bpmndi:BPMNShape>
<bpmndi:BPMNShape bpmnElement="FirstLevel" id="BPMNShape_FirstLevel">
<omgdc:Bounds height="55.0" width="105.0" x="150.0" y="100.0"></omgdc:Bounds>
</bpmndi:BPMNShape>
<bpmndi:BPMNShape bpmnElement="exclusivegateway1" id="BPMNShape_exclusivegateway1">
<omgdc:Bounds height="40.0" width="40.0" x="287.0" y="107.0"></omgdc:Bounds>
</bpmndi:BPMNShape>
<bpmndi:BPMNShape bpmnElement="SecondLevel" id="BPMNShape_SecondLevel">
<omgdc:Bounds height="55.0" width="105.0" x="350.0" y="100.0"></omgdc:Bounds>
</bpmndi:BPMNShape>
<bpmndi:BPMNShape bpmnElement="exclusivegateway2" id="BPMNShape_exclusivegateway2">
<omgdc:Bounds height="40.0" width="40.0" x="488.0" y="107.0"></omgdc:Bounds>
</bpmndi:BPMNShape>
<bpmndi:BPMNShape bpmnElement="ThirdLevel" id="BPMNShape_ThirdLevel">
<omgdc:Bounds height="55.0" width="105.0" x="563.0" y="100.0"></omgdc:Bounds>
</bpmndi:BPMNShape>
<bpmndi:BPMNShape bpmnElement="exclusivegateway3" id="BPMNShape_exclusivegateway3">
<omgdc:Bounds height="40.0" width="40.0" x="699.0" y="107.0"></omgdc:Bounds>
</bpmndi:BPMNShape>
<bpmndi:BPMNShape bpmnElement="endevent1" id="BPMNShape_endevent1">
<omgdc:Bounds height="35.0" width="35.0" x="780.0" y="110.0"></omgdc:Bounds>
</bpmndi:BPMNShape>
<bpmndi:BPMNEdge bpmnElement="flow2" id="BPMNEdge_flow2">
<omgdi:waypoint x="455.0" y="127.0"></omgdi:waypoint>
<omgdi:waypoint x="488.0" y="127.0"></omgdi:waypoint>
</bpmndi:BPMNEdge>
<bpmndi:BPMNEdge bpmnElement="flow3" id="BPMNEdge_flow3">
<omgdi:waypoint x="528.0" y="127.0"></omgdi:waypoint>
<omgdi:waypoint x="563.0" y="127.0"></omgdi:waypoint>
</bpmndi:BPMNEdge>
<bpmndi:BPMNEdge bpmnElement="flow4" id="BPMNEdge_flow4">
<omgdi:waypoint x="327.0" y="127.0"></omgdi:waypoint>
<omgdi:waypoint x="350.0" y="127.0"></omgdi:waypoint>
</bpmndi:BPMNEdge>
<bpmndi:BPMNEdge bpmnElement="flow6" id="BPMNEdge_flow6">
<omgdi:waypoint x="105.0" y="128.0"></omgdi:waypoint>
<omgdi:waypoint x="150.0" y="127.0"></omgdi:waypoint>
</bpmndi:BPMNEdge>
<bpmndi:BPMNEdge bpmnElement="flow7" id="BPMNEdge_flow7">
<omgdi:waypoint x="508.0" y="147.0"></omgdi:waypoint>
<omgdi:waypoint x="507.0" y="204.0"></omgdi:waypoint>
<omgdi:waypoint x="115.0" y="204.0"></omgdi:waypoint>
<omgdi:waypoint x="115.0" y="128.0"></omgdi:waypoint>
<omgdi:waypoint x="150.0" y="127.0"></omgdi:waypoint>
</bpmndi:BPMNEdge>
<bpmndi:BPMNEdge bpmnElement="flow8" id="BPMNEdge_flow8">
<omgdi:waypoint x="668.0" y="127.0"></omgdi:waypoint>
<omgdi:waypoint x="699.0" y="127.0"></omgdi:waypoint>
</bpmndi:BPMNEdge>
<bpmndi:BPMNEdge bpmnElement="flow9" id="BPMNEdge_flow9">
<omgdi:waypoint x="739.0" y="127.0"></omgdi:waypoint>
<omgdi:waypoint x="780.0" y="127.0"></omgdi:waypoint>
</bpmndi:BPMNEdge>
<bpmndi:BPMNEdge bpmnElement="flow10" id="BPMNEdge_flow10">
<omgdi:waypoint x="719.0" y="147.0"></omgdi:waypoint>
<omgdi:waypoint x="718.0" y="187.0"></omgdi:waypoint>
<omgdi:waypoint x="321.0" y="187.0"></omgdi:waypoint>
<omgdi:waypoint x="321.0" y="129.0"></omgdi:waypoint>
<omgdi:waypoint x="350.0" y="127.0"></omgdi:waypoint>
</bpmndi:BPMNEdge>
</bpmndi:BPMNPlane>
</bpmndi:BPMNDiagram>
</definitions>
