I want to define a promotion rule(s) for specific users and specific product. Promotion rule is valid for specific period - it depends on the user.

For example
User A has a 50% discount for product X between 1 Mar 2024 - 8 Mar 2024
User B has a 50% discount for product X between 1 Apr 2024 - 8 Apr 2024
etc.
I was thinking about defining custom Marketing->Promotion rules for each user.

I'll set promotion start-end dates and set custom rule like that for Promotion Type: product:
<xsl:transform version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
      <xsl:template match="/">
        <out>
          <promotionPrice>
            <xsl:if test="in/product/productVariant/productVariantID = 26 and /in/user/username = 'username_of_user_A'">
                <xsl:value-of select="0.50 * in/product/productVariant/price" />
            </xsl:if>
          </promotionPrice>
        </out>
      </xsl:template>
    </xsl:transform>

But it doesn't work. Price for logged in user is displayed without discount on Product List/Cart/Checkout. 
Any ideas why?