RMaaS

The documentation https://httpd.apache.org/docs/2.4/mod/mod_proxy.html#proxypass offers two options:

Alternative 1:

Ordering ProxyPass Directives

The configured ProxyPass and ProxyPassMatch rules are checked in the order of configuration. The first rule that matches wins. So usually you should sort conflicting ProxyPass rules starting with the longest URLs first. Otherwise, later rules for longer URLS will be hidden by any earlier rule which uses a leading substring of the URL. Note that there is some relation with worker sharing.

In other words order matters and your ProxyPass directives should be ordered as below:

<VirtualHost *:443>
    ServerName example.domain.com

    ProxyPass "/api" "http://localhost:3001/api"
    ProxyPassReverse "/api" "http://localhost:3001/api"

    ProxyPass "/" "http://localhost:3000"
    ...

</VirtualHost>

Alternative 2:

Ordering ProxyPass Directives in <Location>s

Only one ProxyPass directive can be placed in a Location block, and the most specific location will take precedence.

In other words when using Location block syntax the ordering doesn't matter and the effect should be the same when you switch the two location blocks around:

<VirtualHost *:443>
    ServerName example.domain.com

    <Location "/">
       ProxyPass  "http://localhost:3000"
       ProxyPassReverse  "http://localhost:3000"
    </Location>

    <Location "/api">
       ProxyPass  "http://localhost:3001/api"
       ProxyPassReverse  "http://localhost:3001/api"
    </Location>
</VirtualHost