GA/GTM Custom Dimension Error (Undefined) - google-analytics

Question

kindly ask you to help me with custom dimensions, as i'm newbie for GA/GTM and did everything per manual.
1) So i created 3 new dimensions for ecommerce in GA:
here is dimensions from GA with indexes
2) I've created snipped in GA and added it into head section of my site:
<script> gtag('event', 'page_view', {
'send_to': 'AW-XXXXXXX',
'ecomm_pagetype': 'page_type',
'ecomm_prodid': 'product_ids',
'ecomm_totalvalue': 'total_value',
'user_id': ‘userId’ }); </script>
along with global site tag.
3) Finally i've created new variables in GTM:
for example for page_type
and in Tag itself.
but i constantly getting error on debug:
{index: '1', dimension:undefined}
screenshot is here
will really appreciate any help!
p.s. sorry for links with images instead embedding, i have not enough reputation here yet.

Answer 1

You clearly are mistaken the gtag which stands for global site tag with the tag manager code.
Instead of using gtag use dataLayer.push, this is the method to push information to Google Tag Manager.
An example:
dataLayer.push({
'ecomm_pagetype' : Variable1,
'ecomm_prodid' : Variable2,
'ecomm_totalvalue' : Variable3
});
Here you have the docs for further reference: docs
Remember to place this tag under the Tag Manager snippet. or remember to initialize an empty dataLayer as the doc states.

Answer 2

Code on page
On your page, before your GTM container snippet add the following (I've used sample values for type, id and value), your code should look like below:
<script>
dataLayer = [{
'ecomm_pagetype': 'MyPageType',
'ecomm_prodid': 'EXAMPLE0000001',
'ecomm_totalvalue': '4000',
}];
</script>
<!-- Google Tag Manager -->
<script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
})(window,document,'script','dataLayer','GTM-XXXXXX');</script>
<!-- End Google Tag Manager -->
GTM - Data Layer Variables
In GTM, create 3 data layer variables for "ecomm_pagetype", "ecomm_prodid", "ecomm_totalvalue" like so:
Type in the key(name) that's in the datalyer object, you can set a default value if you like, otherwise, it will be "undefined" for pages without this variable defined.
Next create a "Google Analytics Settings" variable, this is to simply GA tag configuration, we will link the custom dimensions here.
Put in your own GA property ID, under "More Settings" expand to "Custom Dimensions", click on "ADD CUSTOM DIMENSION". Put in "1" for to reference the index for "ecomm_pagetype" CD in GA. For value, use the variable we created earlier. Do this for all 3 CDs.
Now your Variables page should look something like this:
GTM - Tags, adding CDs to GA tag
Now for your tag. You should have a Google Analytics tag configured in GTM. Looks like you know how to do that, to add the custom dimensions by using the new "My GA Variable" under "Google Analytics Settings". Don't forget to have this trigger on "All pages" or pick your own trigger as you see fit.