Are you seeing the below auth mes
It looks like you've entered the full store URL into the VendHQ system settings in DSYNC. storename.vendhq.com.vendhq.com
Only the first part (store name) should be entered in the system settings:
Solution: log into DSYNC, click on the vend container on the right then click settings and then under store address then enter only the first part of the storename.