Mute black when professionally printed

[maeandfern]

Hello,

I'm pretty new to digital art and I'm really struggling with how to correctly have a document set up to later be professionally printed. When I had my artwork printed, the blacks were very muted. I contacted them and they said I was potentially using black rather than rich blacks. I have tried researching this for hours but with no luck when reprinting my art, it is still always very muted. I previously ordered samples from this company and they do have the ability to print very dark black so unsure why mine turn out almost pale grey. I send the document to them in a PDF format. I have attached both the PDF and the affinity designer file to this.

Any help would be hugely appreciated as I feel like I must be making a simple mistake that I just can't seem to work out. The company I'm printing with is Mixam.

Thanks

Sleipnir_Final.afdesign Sleipnir.pdf

[lacerto]

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