E-mail template

-- url of the page with the problem -- : www.scramble.nl
-- HikaShop version -- : 6.1.1
-- HikaSerial version -- : 6.0.0
-- Joomla version -- : 5.4.1
-- PHP version -- : 8.2
-- Browser(s) name and version -- : Edge 143.0.3650.66

I want to alter the content of the subscription expiration notice. This message is generated in the e-mail template 'Subscription expiration notice' with the code {TXT:SUBSCRIPTION_EXPIRATION_CONTENT}. I tried to alter this content with creating a language override with the constant SUBSCRIPTION_EXPIRATION_CONTENT. But this seems to alter nothing. So the simple question is, how can I change the content of the {TXT:SUBSCRIPTION_EXPIRATION_CONTENT} field in the e-mail template?