Heroku deployment error: No runtime requirements

Question

I am trying to deploy a PHP app on heroku but I get the following error:

remote: 
remote: -----> PHP app detected
remote: -----> Bootstrapping...
remote: -----> Installing platform packages...
remote:        NOTICE: No runtime required in composer.json; requirements
remote:        from dependencies in composer.lock will be used for selection
remote:        - php (7.0.9)
remote:        - apache (2.4.20)
remote:        - nginx (1.8.1)
remote: -----> Installing dependencies...

Apparently only the css is not working, which I find weird since I use the w3.css framework and I am including it via the CDN.

Any ideas?

Answer 1

So, I solved this Runtime warning by adding require: ^7.0.0 in the composer.json.

Kudos to @ElliottFrisch for the hints.