It's a different error now and the function signature is not being matched. You are using an array object where as the function expects a string. You can validate it on the following lines
Example
{{#each context.journey.events.`eventId`._tenant.npoEvent.traject as |s|}}
{%= replaceAll(s.discountedPrice,"([0-9]+\\.[0-9]{2}).*","$1") %}
{{/each}}
Were you able to resolve this query with the given solution or was this something you were able to figure out on your own or do you still need help here? Do let us know.