fontawesome error "Could not find one or more icon"
free-brands-svg-icons use the fab prefix (docs don't appear to mention this, had to check its folder in node_modules), which you have to specify:
<font-awesome-icon :icon="['fab', 'twitter']" class="icon alt"/>When non specified, fas prefix is assumed.
CodeSandbox: https://codesandbox.io/s/6j833qp57k