Hi there @wahlec,
Welcome to the Community and thanks for sharing your question with us!
There are multiple reasons why you might have trouble with this. For instance, are you using a custom theme vs. a free Shopify theme? If so, our documentation on Klaviyo's Back in stock implementation that you linked will only work "out of the box" for Shopify's free default themes. Custom themes will likely require additional web development that you will need to have your developer implement or reach out to a Klaviyo partner to help install this for you if you are not familiar with coding yourself!
However, if you are using a free theme, there are still multiple reasons why changing the replace anchor from false to true isn’t removing your ‘Sold Out’ and replacing it with ‘Notify Me When Available:
Finally, I’d suggest you investigate this additional Community thread to gain more insight on possible problems with BIS.
Thanks for participating in the Community!
-Taylor