I was having the same problem integrating with MOSS, they couldn't locate Supplliers that were listed only as Contacts in Xero. Spend Money Transactions weren't enough for Xero to recognise the Contact was a Supplier.
I found a workaround... By creating a Dummy Bill with xero value, this triggered Xero to recognise this Contact was a Supplier.
I presume the same would work if you created a Dummy Invoice - this should trigger Xero to recognise the Contact is a Customer
I was having the same problem integrating with MOSS, they couldn't locate Supplliers that were listed only as Contacts in Xero. Spend Money Transactions weren't enough for Xero to recognise the Contact was a Supplier.
I found a workaround... By creating a Dummy Bill with xero value, this triggered Xero to recognise this Contact was a Supplier.
I presume the same would work if you created a Dummy Invoice - this should trigger Xero to recognise the Contact is a Customer