Moneris receiving Checkout# rather than Order# from Shopify

[LAR]

We have just integrated Moneris with Shopify and would like the Shopify Order# to come through to Moneris so we can cross-reference the backend of Shopify with paid orders in Moneris. 

For some reason, the Checkout# (at the very beginning of the timeline in orders) is coming through to Moneris instead, which for some reason also includes a period in the string of numbers. 

Shopify and Moneris are both saying the other needs to change how this information is sent/received. 

Is this the correct behaviour? Is anyone using Moneris with Shopify and also not getting the Shopify Order# to Moneris?

Or is there customization that can be made by a developer to the Shopify/Moneris integration?

Thank you!