Applies the template's current version to the active direct debits named in the request (full-overwrite-attach), returning a per-debit result.

With dryRun: true nothing is changed: every requested debit gets a pass, warn or fail result, and unknown or ineligible codes come back as fail rows rather than an error. Without it the request is all-or-nothing: if any requested debit fails a rule (e.g. exceeds the authorised amount, already on the current version, fixed-total/variable, or an unknown code) the entire request is rejected with 422 identifying the offending codes, and nothing is applied. dryRun defaults to false, so omitting it applies the template. When the template is applied, each customer whose recurring amount or frequency changes is emailed the new details.

In both modes an unknown template returns 404, and a fixed-total or yearly template is rejected with 422.