Is Zoho Flow for creating purchase order in Zoho Books is missing a critical field?

Is Zoho Flow for creating purchase order in Zoho Books is missing a critical field?

I am using Zoho Flow to create a purchase order in Zoho Books. Unfortunately, I am getting the following error message: Zoho Books says "Invalid value passed for Customer ID""

If you look at all the field available (see below) in this flow, there is no Customer ID, just Delivery customer ID. I have tried to use the Delivery Customer ID, but still getting the error.

Please advise.

Variables in the Create Purchase flow:
  1. Variable Name 
  2. Organization 
  3. Vendor ID 
  4. Custom Value for Vendor ID 
  5. Contact persons
  6. Billing address ID
  7. Destination of supply
  8. Source of supply
  9. Tax treatment
  10. VAT treatment
  11. Place of supply
  12. Branch
  13. Delivery org address ID
  14. Attention
  15. Delivery customer ID
  16. Delivery customer address ID
  17. Ignorer auto number generation?
  18. Purchaseorder number
  19. Reference number
  20. Date
  21. Delivery date
  22. Payment terms
  23. Ship via
  24. Is reverse charge applied?
  25. Is inclusive tax?
  26. Exchange rate
  27. Pricebook
  28. Item ID
  29. Item name
  30. Item description
  31. Item account ID
  32. Item quantity
  33. Item rate
  34. Tax ID
  35. Tax exemption_code
  36. Discount
  37. Discount account ID
  38. Is discount before tax?
  39. Adjustment description
  40. Adjustment
  41. Customer notes
  42. Terms and conditions
  43. Template ID