I have looked through many of the forum posts but just can't put my finger on what the Discount__c field has to do with Step #4.

I get the following error followed by an email:

Challenge Not yet complete... here's what's wrong: 
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_EXECUTE_FLOW_TRIGGER, The record couldn’t be saved because it failed to trigger a flow. A flow trigger failed to execute the flow with version ID 3011I000000PJU7. Flow error messages: An unhandled fault has occurred in this flow
An unhandled fault has occurred while processing the flow. Please contact your system administrator for more information. Contact your administrator for help.: []

the email:

Error element myRule_1_A1 (FlowRecordCreate).
This error occurred when the flow tried to create records: REQUIRED_FIELD_MISSING: Required fields are missing: [Discount__c]. For details, see API Exceptions.
This report lists the elements that the flow interview executed. The report is a beta feature.
We welcome your feedback on IdeaExchange.
Flow Details
Flow Name: Fulfillment_Creation
Type: Workflow
Version: 4
Status: Active
Flow Interview Details
Interview Label: Fulfillment_Creation-4_InterviewLabel
Current User: Jeroen van den Eijkhof (0051I000000qFJl)
Start time: 10/3/2017 7:55 PM
Duration: 0 seconds
How the Interview Started
Jeroen van den Eijkhof (0051I000000qFJl) started the flow interview.
Some of this flow's variables were set when the interview started.
myVariable_old = null
myVariable_current = 00k1I00000AepL1QAJ
ASSIGNMENT: myVariable_waitStartTimeAssignment
{!myVariable_waitStartTimeVariable} Equals {!Flow.CurrentDateTime}
Result
{!myVariable_waitStartTimeVariable} = "10/3/2017 7:55 PM"
DECISION: myPreWaitDecision_myWait_myRule_1
Executed this outcome: myPreWaitRule_myWait_myRule_1
Outcome conditions: and
1. {!myVariable_current.Opportunity.StageName} (New) Does not equal Cancelled
2. {!myVariable_current.Fulfillment_Created__c} (false) Equals false
Logic: All conditions must be true (AND)
DECISION: myDecision
Executed this outcome: myRule_1
Outcome conditions: and
1. {!myVariable_current.Opportunity.StageName} (New) Does not equal Cancelled
2. {!myVariable_current.Fulfillment_Created__c} (false) Equals false
Logic: All conditions must be true (AND)
RECORD CREATE: myRule_1_A1
Create one Fulfillment__c record where:
AdventurePackageId__c = {!myVariable_current.Id} (00k1I00000AepL1QAJ)
Adventure_Package_Cost__c = {!myVariable_current.TotalPrice} (1)
Adventure__c = {!myVariable_current.Product2Id} (01t1I000000IoClQAK)
Expedition_Leader__c = {!myVariable_current.Product2.Expedition_Leader__c} (null)
Explorer__c = {!myVariable_current.Explorer__c} (0031I000002pnbsQAA)
Name = {!formula_2_myRule_1_A1_8225086771} (Lemons00k1I00000AepL1QAJ)
Opportunity__c = {!myVariable_current.OpportunityId} (0061I000002RhpDQAS)
Schedule_Date__c = {!myVariable_current.ServiceDate} (January 1, 2050)
Status__c = New
Result
Failed to create record.

Error Occurred: This error occurred when the flow tried to create records: REQUIRED_FIELD_MISSING: Required fields are missing: [Discount__c]. For details, see API Exceptions.

I have the Discount_c field on the Opportunity object and it is set to required as well as defaulted to 0.
Your help is appreciated!