In the first example under https://bootstrap-vue.js.org/docs/components/form/#inline-form, the <b-input-group left="@" class="mb-2 mr-sm-2 mb-sm-0"> part doesn't seem right. I suppose this was supposed to provide an example of the "prepend" attribute - I don't think "left" is a valid attribute.

Suggested change:

<b-input-group prepend="@" class="mb-2 mr-sm-2 mb-sm-0">