Links in email not working in inbox

Question

I have a data extension that contains customers along with a category. In my html content, I want to add the category for the customer IF the customer_id can be found within that data extension. If it can't be found in the data extension then to handle this with default category. To do this I'm using LookupRows. My code and the links work within SF preview and test function but when the email is sent to my inbox and I click on the link in my inbox, it leads to a page with the below error. I've also tried personalisation string, to use redirect only but it doesn't work.

Error:

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Here is my FINAL working code:

%%[

  VAR @category_name_look_up, @category_link_look_up, @category_url_tracked, @rows, @row, @rowCount, @customer_id

  SET @category_name_look_up = Lookup("Customer Data Extension", "category", "customer_id", customer_id)
  SET @category_link_look_up = Lookup("Customer Data Extension", "category_link", "customer_id", customer_id)
  SET @category_url_tracked = CONCAT(@category_link_look_up,"?utm_source=salesforce&utm_campaign=&utm_term=marhead|default|01")

  SET @rows = LookupRows("Customer Data Extension","customer_id", @customer_id)
  SET @rowCount = rowcount(@rows)
  SET @customer_id = AttributeValue("customer_id")

  if @rowCount > 0 then

]%%

    <td align="center">
        <a href="%%=RedirectTo(@category_url_tracked)=%%">%%=v(@category_name_look_up)=%%</a>
    </td>

%%[ELSE]%%

    <td align="center">
        <a href="https://www.website.com/shop/this_category?utm_source=salesforce&utm_campaign=&utm_term=marhead|default|01">This Category</a>
    </td>

%%[ENDIF]%%

Answer 1

I think you have to build the entire url you want to redirectTo before calling the function.

Make the tracking params part of variable @category_link_look_up, then

<a href="%%=RedirectTo(@category_link_look_up)=%%">click</a>

(without TreatAsContent)

Answer 2

I am assuming the link you are pulling from the DE contains ampscript or personalization strings which is why you are using TreatAsContent. As @jonaslamberty said, you need to have the final url before using the redirectto

So I would recommend putting in a new var to CONCAT it together first, use the following instead:

SET @myUrl = CONCAT(TreatAsContent(@category_link_look_up),"?utm_source=salesforce&utm_campaign=&utm_term=marhead|default|01")

<a href="%%=RedirectTo(@myUrl)=%%">%%=v(@category_name_look_up)=%%</a>