Replacing a substring with selected value

Hello,

I'm creating a personalized letter in Power BI desktop (have to do it using this, because of client's demand...).

I have a customer table (lets say it has only 2 columns: custID and custName), and an independant text-parts table that composes the letter.

In these text-parts, there are place-holders for parameters. They look like "[param-name]".

For this example, I have 2 types of place-holders: [year] and [custName].

So a typical text-part could look like: "During the year of [year], the above-mentioned [custName] has purchased items..."

The report has to replace [year] with a fixed value (2022) and [custName] with a value from customers table, after filtering (page filter or slicer) only one customer.

I created another table, name "params", which holds 2022 as a value, and  managed the [year] substitution well with:

substitute([text],"[year]",calculate(max('params'[value]),filter('params',[param]="year"))).

However, when trying to substitute with custName, I always get the unfiltered customer list.

Tried these, with no avail:

- substitute([text],"[custName]",max('customers'[custName]))

- substitute([text],"[custName]",calculate(maxx('customers'[custName]),keepfilters(not(isblank('customers'[custName])))))

- substitute([text],"[custName]",selectedvalue('customers'[custName]))

- substitute([text],"[custName]",maxx(filter('customers',[custName]=selectedvalue('customers'[custName])),'customers'[custName]))

Any ideas?