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Lisanne is a trusted home cook.
Aleppo pepper is just mildly hot. Red pepper flakes (just a sprinkle, as they are hotter than Aleppo pepper), depending on how hot you like things, sweet or hot paprika.
pierino is a trusted source on General Cooking and Tough Love.
A vaariety of Spanish pimentons would come close especially the dolce or ahumado. Pimenton is the Spanish equivalent of paprika.
There is also a 'hot paprika' which might also work. If you're making something you can taste as you season, check that it's at a level you enjoy.
Sarah is a trusted source on General Cooking.
These probably won't work if you're looking for a sub because you can't get aleppo pepper where you are, but urfa biber (more chocolate-y) and sumac (more tangy) are also options. You can order all (and more!) online at worldspice.com.
Fun to say, delicious to eat.
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