Error when deploying php/node monorepo

Hello, using digitalocean/sample-monorepo .do/app.yaml as a guide I’ve created an app spec for my monorepo Stirreg/do-app-platform-monorepo.

During build everything seems fine, but when deploying I get the following errors in my logs:

api      | 18:26:11 DOCUMENT_ROOT changed to 'public/'
api      | 18:26:11 Using Nginx server-level configuration include 'nginx.conf'
api      | 18:26:12 Assuming 512MB of RAM
api      | 18:26:12 PHP memory_limit is 128M Bytes
api      | 18:26:12 Starting php-fpm with 4 workers...
api      | 18:26:14 [02-Mar-2021 17:26:14] WARNING: Nothing matches the include pattern '/app/.heroku/php/' from /workspace/api/vendor/heroku/heroku-buildpack-php/conf/php/8/php-fpm.conf at line 596.
api      | 18:26:14 Starting nginx...
api      | 18:26:14 nginx: [alert] could not open error log file: open() "/app/.heroku/php/var/log/nginx/error.log" failed (2: No such file or directory)
api      | 18:26:14 2021/03/02 17:26:14 [emerg] 166#0: mkdir() "/app/.heroku/php/var/run/nginx/client_body_temp" failed (2: No such file or directory)
api      | 18:26:14 Process exited unexpectedly: nginx, shutting down...
api      | 18:26:14 Stopping php-fpm...
api      | 18:26:14 Shutdown complete.

I suspect a mismatch in paths when using a source_dir with a monorepo. Is it possible to get this running?