HTTP error "URL Parameter error" for fal.ai request id

Welcome to the Make community!

Firstly, you need to select the concat function from the variables panel.

Secondly, you do not need to use a function here as variables and strings will be automatically joined together in a text field.

Here are some useful links and guides you can use to learn more on how to use the Make platform, apps, and app modules. I found these useful when I was learning Make, and hope they might benefit you too —

Getting Started

Help Centre Basics

Articles & Videos

Hope this helps! Let me know if there are any further questions or issues.

— @samliew

P.S.: Investing some effort into the Make Academy will save you lots of time and frustration using Make.