When I try to debug the flow, I get a Conflict error.

Hi.  I have a question about the "Create a flow using an external service action" challenge in the "Using external services in a flow" section of the Trailhead "Intermediate System Administrator" course. 

I followed the instructions to set it up, but when I debug the flow I get an error saying "Conflict." 

The same error occurred even after creating a new Playground. 

for some reason the challenge itself is passed. 

I would be grateful if you could let me know how to solve the above problem. Thank you in advance. 

<Error details during debugging> 

BANKSERVICE.ADDACCOUNT (EXTERNAL SERVICES):

Add Bank Account 

Inputs:

accountName = {!Last_Name_on_Account} (Thompson) 

accountType = {!Bank_Account_Type} (Checking)

Error Occurred: Conflict 

<Contents of received email> 

You’ve received this email because an error occurred while your "Bank Account Records" flow was running. Debug this flow in Flow Builder. 

Error element Add_Bank_Account (FlowActionCall). 

Conflict