What should I ask my graphic designer for?

Short answer: The SVG file of your logo: it is the only one that really matters, and it uploads as it is. Failing that, a 4000 px / 300 dpi PNG with a transparent background. And if your logo is dark or very colorful, a negative version or one with an outline.

The list to hand over

The SVG file. This is the main request, and it is a simple re-export from the file the logo was drawn in. You then upload it exactly as it is: no pixel dimensions and no resolution to keep an eye on, and it will serve every marking, from the heart placement to a large back print.
Failing that: a PNG, 4000 px on the longest side, 300 dpi, with a transparent background. This is the fallback if no SVG is available — it freezes the logo at one given size.
A negative version, or one with an outline (white, black or another color), so the logo stays readable on product colors close to its own.
No transparency in the colors: gradients between solid colors are fine, but no gradient fading to transparent. Transparency only exists on screen, never on a physical marking.
No isolated element smaller than 0.3 mm once the logo is at its real print size — see The small details of my logo disappear when printed.

Ask for “a real SVG”

An SVG can be nothing more than a bitmap image in a vector wrapper — a logo simply “saved as SVG” without being redrawn. Ask explicitly for an SVG the logo is drawn in, with the fonts converted to outlines and no embedded image. Otherwise the file will give you nothing more than the PNG you already have — see My file is an SVG or a PDF but you say it is not vector.

This is the one brief to send before the work starts. Almost every logo problem that comes up later traces back to one of these five points.

If your graphic designer works in Illustrator

They will naturally hand you an AI or an EPS, neither of which can be uploaded to the site. Ask for the SVG export as well: it is the same operation for them, and it leaves you self-sufficient. If they cannot, send us their file — see How do I send you my logo if I have no print file.

Going further

You'll know it worked when: You receive an SVG file you can upload as it is — or, failing that, a PNG that meets the brief.