Profile: Support

I need to think.
Write me on Monday

I didn't understand you.

>Im using standard checkout on nopCommerce 3.8

1. One page checkout or multipages?
2. Do you any external theme? Maybe the theme developer used another HTML markup for "Buy" button. Can you ZIP your theme and send me it to my email?

'Include Tax'  - this parameter is for product prices.

transactionTotal - order total with tax and shipping fees.
transactionTax - order total tax.

I can add the new parameter 'transactionSubTotal'
transactionTotal - order subtotal value (with or without TAX)
What do you think?

The problem was in TLC1.2
Read this topic
https://stackoverflow.com/questions/34920429/is-tls-1-1-and-tls-1-2-enabled-by-default-for-net-4-5-and-net-4-5-1

You didn't enable TLC1.2 for nop store.
I did it in new release of plugin.  Download the new one and try it.
Write me about result.

Please check if this product Product A1.1 (and this Product A1.2  too )is in another category in one time (ex. in several catogories).

Write me I wait.

Please check it again.
Maybe you saw the feed file from browser's cache.

  <FeedAttribute>
    <Id>31</Id>
    <FeedCaption>Custom label for Shopping Campaigns 0</FeedCaption>
    <FeedName>custom_label_0</FeedName>
    <FieldNameCode>productcost</FieldNameCode>
    <ConvertValues />
    <CharsLimit>100</CharsLimit>
    <Required>false</Required>
    <IgnoreNullOrEmpty>false</IgnoreNullOrEmpty>
    <UseCDATA>false</UseCDATA>
    <ActionId>0</ActionId>
    <AdvancedField>true</AdvancedField>
    <RowSourceType>0</RowSourceType>
    <AttributeControlType>0</AttributeControlType>
  </FeedAttribute>

ID is unique key for each field.
Change it with value 45645654 and try.

Check if you has
<Id>51</Id>
only one time.
Maybe you copy existing ID and this template has two items with ID 51