Simple tooltip on button not working

I want a simple tooltip to pop up when hovering over a button. I have tried the following but no popup appears, can anyone help?

<a href="#" class="btn btn-sm flex-grow-1 mr-1 ml-1 mt-1 mb-1" dmx-on:click="browser1.goto('call_pdf_generate.php?job_id='+query1.data.job_id)" dmx-class:btn-outline-danger="(steps.value != 22)" dmx-bs-tooltip="'Have you saved before generating PDF?'">11. Create PDF <i class="far fa-file-pdf fa-lg fa-fw icon"></i></a>