The only way to use cash credit to pay for membership is by doing it manually as far as I know.
I.e. you buy the memberhip manually and pay for it from your cash credit balance.
Hope this helps.
If you qualify for it then it should happen automatically.
https://48.ie/recruit-and-reward
If it doesn't then contact 48 support.
See the link in my signature below.
Hope this helps.
While you're here, check out our "Featured Topics" below.
Our Troubleshooting Guide and Knowledgebase contain help and support articles and popular questions to help you as a 48 customer.